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The KA9Q Internet Software Package
Updated for 890421.1 Revision
May 8, 1989
by
Bdale Garbee, N3EUA
Copyright 1989 by Bdale Garbee.
All Rights Reserved.
This Document may be reproduced in whole
or in part for any non-commercial purpose,
as long as credit is given the author.
- 2 -
Caveat Emptor
This document is a major rewrite of the document included with 871225.0
release of the KA9Q package, but it is in the author's opinion very far
from perfect. I believe that the bulk of the material here is factually
correct, but the formatting is rough, and there are no doubt some juicy
tidbits missing that should have been included.
I would greatly appreciate reports of problems with the documentation,
particularly if they are accompanied by suggested fixes! I promise to
back up the document sources this time around, so that disk crashes
won't force me to start over from scratch (which is what happened this
time...).
If you have comments or suggestions about the documentation, contact me
via email at bdale@col.hp.com on the Internet, ...!winfree!bdale via
UUCP, or as 76430,3323 on Compuserve.
My profound thanks to the folks who contributed to this release, partic-
ularly Bob Hoffman N3CVL and Ron Henderson WA7TAS, without whom it would
have been impossible.
Bdale Garbee, N3EUA
- 3 -
1. Introduction to TCP/IP and the KA9Q Software
This document describes the KA9Q Internet Package, which is an implemen-
tation of the network protocol family originally created as part of the
Arpanet project. The protocol family is commonly refered to as "TCP/IP",
acronyms for two of the many protocols included.
The KA9Q package is the result of several years of development by Phil
Karn, KA9Q, and his "merry band of implementors". The "TCP group" has
grown to include hundreds of individuals worldwide, many of whom have
contributed ideas and software to this release. All of the sources to
the software are included, and interested parties are encouraged to
experiment and contribute changes resulting from their efforts back to
the group. This is discussed further in the technical appendix.
1.1. An Overview of the TCP/IP Protocol Family
Following is an overview of the protocol family supported by the KA9Q
package. While reading this section will give you a wonderful overview
of what's going on, you can feel free to skip ahead and try out the pro-
gram first, then come back and read this section to flesh out your
understanding.
1.1.1. Acknowledgement
The material in this section was adapted from a document written by
Charles L. Hedrick, of RUTGERS, The State University of New Jersey. The
original document was Copyright 1987 by Charles L. Hedrick, and the
material excerpted for this section is used by permission.
1.1.2. Introduction
This document is a brief introduction to TCP/IP, followed by advice on
what to read for more information. This is not intended to be a
complete description. It can give you a reasonable idea of the
capabilities of the protocols. But if you need to know any details of
the technology, you will want to read the standards yourself.
Throughout the text, you will find references to the standards, in the
form of "RFC" or "IEN" numbers. These are document numbers. The final
section of this document tells you how to get copies of those
standards.
1.1.3. What is TCP/IP?
TCP/IP is a set of protocols developed to allow cooperating computers
to share resources across a network. It was developed by a community of
researchers centered around the ARPAnet. Certainly the ARPAnet is the
best-known TCP/IP network. However as of June, 87, at least 130 dif-
ferent vendors had products that support TCP/IP, and thousands of net-
works of all kinds use it. Over time, the original ARPAnet has been
phased out, and is being replaced by a variety of networks running the
same protocols loosely referred to as "The Internet".
First some basic definitions. The most accurate name for the set of
- 4 -
protocols we are describing is the "Internet protocol suite". TCP and IP
are two of the protocols in this suite. (They will be described
below.) Because TCP and IP are the best known of the protocols, it has
become common to use the term TCP/IP or IP/TCP to refer to the whole
family. It is probably not worth fighting this habit. However this can
lead to some oddities. For example, I find myself talking about NFS
as being based on TCP/IP, even though it doesn't use TCP at all. (It
does use IP. But it uses an alternative protocol, UDP, instead of
TCP. All of this alphabet soup will be unscrambled in the following
pages.)
The Internet is a collection of networks, including the Arpanet,
NSFnet, regional networks such as NYsernet, local networks at a number
of University and research institutions, and a number of military
networks. The term "Internet" applies to this entire set of networks.
The subset of them that is managed by the Department of Defense is
referred to as the "DDN" (Defense Data Network). This includes some
research-oriented networks, such as the Arpanet, as well as more
strictly military ones. (Because much of the funding for Internet pro-
tocol developments is done via the DDN organization, the terms
Internet and DDN can sometimes seem equivalent.) All of these net-
works are connected to each other. Users can send messages from any
of them to any other, except where there are security or other policy
restrictions on access. Officially speaking, the Internet protocol
documents are simply standards adopted by the Internet community
for its own use. More recently, the Department of Defense issued a
MILSPEC definition of TCP/IP. This was intended to be a more formal
definition, appropriate for use in purchasing specifications. However
most of the TCP/IP community continues to use the Internet standards.
The MILSPEC version is intended to be consistent with it.
Whatever it is called, TCP/IP is a family of protocols. A few provide
"low-level" functions needed for many applications. These include IP,
TCP, and UDP. (These will be described in a bit more detail later.)
Others are protocols for doing specific tasks, e.g. transferring files
between computers, sending mail, or finding out who is logged in on
another computer. Initially TCP/IP was used mostly between mini-
computers or mainframes. These machines had their own disks, and gen-
erally were self-contained. Thus the most important "traditional"
TCP/IP services are:
- file transfer. The file transfer protocol (FTP) allows a user on
any computer to get files from another computer, or to send files
to another computer. Security is handled by requiring the user
to specify a user name and password for the other computer.
Provisions are made for handling file transfer between machines
with different character set, end of line conventions, etc. This
is not quite the same thing as more recent "network file system"
or "netbios" protocols, which will be described below. Rather,
FTP is a utility that you run any time you want to access a file
on another system. You use it to copy the file to your own
system. You then work with the local copy. (See RFC 959 for
specifications for FTP.)
- 5 -
- remote login. The network terminal protocol (TELNET) allows a
user to log in on any other computer on the network. You start a
remote session by specifying a computer to connect to. From that
time until you finish the session, anything you type is sent to
the other computer. Note that you are really still talking to
your own computer. But the telnet program effectively makes your
computer invisible while it is running. Every character you type
is sent directly to the other system. Generally, the connection
to the remote computer behaves much like a dialup connection.
That is, the remote system will ask you to log in and give a
password, in whatever manner it would normally ask a user who had
just dialed it up. When you log off of the other computer, the
telnet program exits, and you will find yourself talking to your
own computer. Microcomputer implementations of telnet generally
include a terminal emulator for some common type of terminal.
(See RFC's 854 and 855 for specifications for telnet. By the
way, the telnet protocol should not be confused with Telenet, a
vendor of commercial network services.)
- computer mail. This allows you to send messages to users on
other computers. Originally, people tended to use only one or
two specific computers. They would maintain "mail files" on
those machines. The computer mail system is simply a way for you
to add a message to another user's mail file. There are some
problems with this in an environment where microcomputers are
used. The most serious is that a micro is not well suited to
receive computer mail. When you send mail, the mail software
expects to be able to open a connection to the addressee's
computer, in order to send the mail. If this is a microcomputer,
it may be turned off, or it may be running an application other
than the mail system. For this reason, mail is normally handled
by a larger system, where it is practical to have a mail server
running all the time. Microcomputer mail software then becomes a
user interface that retrieves mail from the mail server. (See
RFC 821 and 822 for specifications for computer mail. See RFC
937 for a protocol designed for microcomputers to use in reading
mail from a mail server.)
These services should be present in any implementation of TCP/IP,
except that micro-oriented implementations may not support computer
mail. These traditional applications still play a very important role in
TCP/IP-based networks. However more recently, the way in which net-
works are used has been changing. The older model of a number of
large, self-sufficient computers is beginning to change. Now many
installations have several kinds of computers, including
microcomputers, workstations, minicomputers, and mainframes. These com-
puters are likely to be configured to perform specialized tasks.
Although people are still likely to work with one specific computer,
that computer will call on other systems on the net for specialized
services. This has led to the "server/client" model of network
services. A server is a system that provides a specific service for the
rest of the network. A client is another system that uses that ser-
vice. (Note that the server and client need not be on different comput-
ers. They could be different programs running on the same
- 6 -
computer.) Here are the kinds of servers typically present in a
modern computer setup. Note that these computer services can all be
provided within the framework of TCP/IP.
- network file systems. This allows a system to access files on
another computer in a somewhat more closely integrated fashion
than FTP. A network file system provides the illusion that disks
or other devices from one system are directly connected to other
systems. There is no need to use a special network utility to
access a file on another system. Your computer simply thinks it
has some extra disk drives. These extra "virtual" drives refer
to the other system's disks. This capability is useful for
several different purposes. It lets you put large disks on a few
computers, but still give others access to the disk space. Aside
from the obvious economic benefits, this allows people working on
several computers to share common files. It makes system
maintenance and backup easier, because you don't have to worry
about updating and backing up copies on lots of different
machines. A number of vendors now offer high-performance
diskless computers. These computers have no disk drives at all.
They are entirely dependent upon disks attached to common "file
servers". (See RFC's 1001 and 1002 for a description of
PC-oriented NetBIOS over TCP. In the workstation and
minicomputer area, Sun's Network File System is more likely to be
used. Protocol specifications for it are available from Sun
Microsystems.)
- remote printing. This allows you to access printers on other
computers as if they were directly attached to yours. (The most
commonly used protocol is the remote lineprinter protocol from
Berkeley Unix. Unfortunately, there is no protocol document for
this. However the C code is easily obtained from Berkeley, so
implementations are common.)
- remote execution. This allows you to request that a particular
program be run on a different computer. This is useful when you
can do most of your work on a small computer, but a few tasks
require the resources of a larger system. There are a number of
different kinds of remote execution. Some operate on a command
by command basis. That is, you request that a specific command
or set of commands should run on some specific computer. (More
sophisticated versions will choose a system that happens to be
free.) However there are also "remote procedure call" systems
that allow a program to call a subroutine that will run on
another computer. (There are many protocols of this sort.
Berkeley Unix contains two servers to execute commands remotely:
rsh and rexec. The man pages describe the protocols that they
use. The user-contributed software with Berkeley 4.3 contains a
"distributed shell" that will distribute tasks among a set of
systems, depending upon load. Remote procedure call mechanisms
have been a topic for research for a number of years, so many
organizations have implementations of such facilities. The most
widespread commercially-supported remote procedure call protocols
seem to be Xerox's Courier and Sun's RPC. Protocol documents are
- 7 -
available from Xerox and Sun. There is a public implementation
of Courier over TCP as part of the user-contributed software with
Berkeley 4.3. An implementation of RPC was posted to Usenet by
Sun, and also appears as part of the user-contributed software
with Berkeley 4.3.)
- name servers. In large installations, there are a number of
different collections of names that have to be managed. This
includes users and their passwords, names and network addresses
for computers, and accounts. It becomes very tedious to keep
this data up to date on all of the computers. Thus the databases
are kept on a small number of systems. Other systems access the
data over the network. (RFC 822 and 823 describe the name server
protocol used to keep track of host names and Internet addresses
on the Internet. This is now a required part of any TCP/IP
implementation. IEN 116 describes an older name server protocol
that is used by a few terminal servers and other products to look
up host names. Sun's Yellow Pages system is designed as a
general mechanism to handle user names, file sharing groups, and
other databases commonly used by Unix systems. It is widely
available commercially. Its protocol definition is available
from Sun.)
- terminal servers. Many installations no longer connect terminals
directly to computers. Instead they connect them to terminal
servers. A terminal server is simply a small computer that only
knows how to run telnet (or some other protocol to do remote
login). If your terminal is connected to one of these, you
simply type the name of a computer, and you are connected to it.
Generally it is possible to have active connections to more than
one computer at the same time. The terminal server will have
provisions to switch between connections rapidly, and to notify
you when output is waiting for another connection. (Terminal
servers use the telnet protocol, already mentioned. However any
real terminal server will also have to support name service and a
number of other protocols.)
- network-oriented window systems. Until recently, high-
performance graphics programs had to execute on a computer that
had a bit-mapped graphics screen directly attached to it.
Network window systems allow a program to use a display on a
different computer. Full-scale network window systems provide an
interface that lets you distribute jobs to the systems that are
best suited to handle them, but still give you a single
graphically-based user interface. (The most widely-implemented
window system is X. A protocol description is available from
MIT's Project Athena. A reference implementation is publically
available from MIT. A number of vendors are also supporting
NeWS, a window system defined by Sun. Both of these systems are
designed to use TCP/IP.)
Note that some of the protocols described above were designed by
Berkeley, Sun, or other organizations. Thus they are not officially
part of the Internet protocol suite. However they are implemented
- 8 -
using TCP/IP, just as normal TCP/IP application protocols are. Since
the protocol definitions are not considered proprietary, and since
commercially-support implementations are widely available, it is
reasonable to think of these protocols as being effectively part of
the Internet suite. Note that the list above is simply a sample of
the sort of services available through TCP/IP. However it does
contain the majority of the "major" applications. The other
commonly-used protocols tend to be specialized facilities for getting
information of various kinds, such as who is logged in, the time of
day, etc. However if you need a facility that is not listed here, we
encourage you to look through the current edition of Internet
Protocols (currently RFC 1011), which lists all of the available
protocols, and also to look at some of the major TCP/IP
implementations to see what various vendors have added.
1.1.4. General description of the TCP/IP protocols
TCP/IP is a layered set of protocols. In order to understand what
this means, it is useful to look at an example. A typical situation
is sending mail. First, there is a protocol for mail. This defines a
set of commands which one machine sends to another, e.g. commands to
specify who the sender of the message is, who it is being sent to, and
then the text of the message. However this protocol assumes that
there is a way to communicate reliably between the two computers.
Mail, like other application protocols, simply defines a set of
commands and messages to be sent. It is designed to be used together
with TCP and IP. TCP is responsible for making sure that the commands
get through to the other end. It keeps track of what is sent, and
retransmitts anything that did not get through. If any message is too
large for one datagram, e.g. the text of the mail, TCP will split it
up into several datagrams, and make sure that they all arrive
correctly. Since these functions are needed for many applications,
they are put together into a separate protocol, rather than being part
of the specifications for sending mail. You can think of TCP as
forming a library of routines that applications can use when they need
reliable network communications with another computer. Similarly, TCP
calls on the services of IP. Although the services that TCP supplies
are needed by many applications, there are still some kinds of
applications that don't need them. However there are some services
that every application needs. So these services are put together into
IP. As with TCP, you can think of IP as a library of routines that
TCP calls on, but which is also available to applications that don't
use TCP. This strategy of building several levels of protocol is
called "layering". We think of the applications programs such as
mail, TCP, and IP, as being separate "layers", each of which calls on
the services of the layer below it. Generally, TCP/IP applications
use 4 layers:
- an application protocol such as mail
- a protocol such as TCP that provides services need by many
applications
- IP, which provides the basic service of getting datagrams to
- 9 -
their destination
- the protocols needed to manage a specific physical medium, such
as Ethernet or a point to point line.
TCP/IP is based on the "catenet model". (This is described in more
detail in IEN 48.) This model assumes that there are a large number
of independent networks connected together by gateways. The user
should be able to access computers or other resources on any of these
networks. Datagrams will often pass through a dozen different
networks before getting to their final destination. The routing
needed to accomplish this should be completely invisible to the user.
As far as the user is concerned, all he needs to know in order to
access another system is an "Internet address". This is an address
that looks like 128.6.4.194. It is actually a 32-bit number. However
it is normally written as 4 decimal numbers, each representing 8 bits
of the address. (The term "octet" is used by Internet documentation
for such 8-bit chunks. The term "byte" is not used, because TCP/IP is
supported by some computers that have byte sizes other than 8 bits.)
Generally the structure of the address gives you some information
about how to get to the system. For example, 128.6 is a network
number assigned by a central authority to Rutgers University. Rutgers
uses the next octet to indicate which of the campus Ethernets is
involved. 128.6.4 happens to be an Ethernet used by the Computer
Science Department. The last octet allows for up to 254 systems on
each Ethernet. (It is 254 because 0 and 255 are not allowed, for
reasons that will be discussed later.) Note that 128.6.4.194 and
128.6.5.194 would be different systems. The structure of an Internet
address is described in a bit more detail later.
Of course we normally refer to systems by name, rather than by
Internet address. When we specify a name, the network software looks
it up in a database, and comes up with the corresponding Internet
address. Most of the network software deals strictly in terms of the
address. (RFC 882 describes the name server technology used to handle
this lookup.)
TCP/IP is built on "connectionless" technology. Information is
transfered as a sequence of "datagrams". A datagram is a collection
of data that is sent as a single message. Each of these datagrams is
sent through the network individually. There are provisions to open
connections (i.e. to start a conversation that will continue for some
time). However at some level, information from those connections is
broken up into datagrams, and those datagrams are treated by the
network as completely separate. For example, suppose you want to
transfer a 15000 octet file. Most networks can't handle a 15000 octet
datagram. So the protocols will break this up into something like 30
500-octet datagrams. Each of these datagrams will be sent to the
other end. At that point, they will be put back together into the
15000-octet file. However while those datagrams are in transit, the
network doesn't know that there is any connection between them. It is
perfectly possible that datagram 14 will actually arrive before
datagram 13. It is also possible that somewhere in the network, an
error will occur, and some datagram won't get through at all. In that
- 10 -
case, that datagram has to be sent again.
Note by the way that the terms "datagram" and "packet" often seem to
be nearly interchangable. Technically, datagram is the right word to
use when describing TCP/IP. A datagram is a unit of data, which is
what the protocols deal with. A packet is a physical thing, appearing
on an Ethernet or some wire. In most cases a packet simply contains a
datagram, so there is very little difference. However they can
differ. When TCP/IP is used on top of X.25, the X.25 interface breaks
the datagrams up into 128-byte packets. This is invisible to IP,
because the packets are put back together into a single datagram at
the other end before being processed by TCP/IP. So in this case, one
IP datagram would be carried by several packets. However with most
media, there are efficiency advantages to sending one datagram per
packet, and so the distinction tends to vanish.
Two separate protocols are involved in handling TCP/IP datagrams. TCP
(the "transmission control protocol") is responsible for breaking up
the message into datagrams, reassembling them at the other end,
resending anything that gets lost, and putting things back in the
right order. IP (the "internet protocol") is responsible for routing
individual datagrams. It may seem like TCP is doing all the work.
And in small networks that is true. However in the Internet, simply
getting a datagram to its destination can be a complex job. A
connection may require the datagram to go through several networks at
Rutgers, a serial line to the John von Neuman Supercomputer Center, a
couple of Ethernets there, a series of 56Kbaud phone lines to another
NSFnet site, and more Ethernets on another campus. Keeping track of
the routes to all of the destinations and handling incompatibilities
among different transport media turns out to be a complex job. Note
that the interface between TCP and IP is fairly simple. TCP simply
hands IP a datagram with a destination. IP doesn't know how this
datagram relates to any datagram before it or after it.
It may have occurred to you that something is missing here. We have
talked about Internet addresses, but not about how you keep track of
multiple connections to a given system. Clearly it isn't enough to
get a datagram to the right destination. TCP has to know which
connection this datagram is part of. This task is referred to as
"demultiplexing." In fact, there are several levels of demultiplexing
going on in TCP/IP. The information needed to do this demultiplexing
is contained in a series of "headers". A header is simply a few extra
octets tacked onto the beginning of a datagram by some protocol in
order to keep track of it. It's a lot like putting a letter into an
envelope and putting an address on the outside of the envelope.
Except with modern networks it happens several times. It's like you
put the letter into a little envelope, your secretary puts that into a
somewhat bigger envelope, the campus mail center puts that envelope
into a still bigger one, etc. Here is an overview of the headers that
get stuck on a message that passes through a typical TCP/IP network:
We start with a single data stream, say a file you are trying to send
to some other computer:
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......................................................
TCP breaks it up into manageable chunks. (In order to do this, TCP
has to know how large a datagram your network can handle. Actually,
the TCP's at each end say how big a datagram they can handle, and then
they pick the smallest size.)
.... .... .... .... .... .... .... ....
TCP puts a header at the front of each datagram. This header actually
contains at least 20 octets, but the most important ones are a source
and destination "port number" and a "sequence number". The port
numbers are used to keep track of different conversations. Suppose 3
different people are transferring files. Your TCP might allocate port
numbers 1000, 1001, and 1002 to these transfers. When you are sending a
datagram, this becomes the "source" port number, since you are the
source of the datagram. Of course the TCP at the other end has
assigned a port number of its own for the conversation. Your TCP has
to know the port number used by the other end as well. (It finds out
when the connection starts, as we will explain below.) It puts this
in the "destination" port field. Of course if the other end sends a
datagram back to you, the source and destination port numbers will be
reversed, since then it will be the source and you will be the
destination. Each datagram has a sequence number. This is used so
that the other end can make sure that it gets the datagrams in the
right order, and that it hasn't missed any. (See the TCP
specification for details.) TCP doesn't number the datagrams, but the
octets. So if there are 500 octets of data in each datagram, the
first datagram might be numbered 0, the second 500, the next 1000, the
next 1500, etc. Finally, I will mention the Checksum. This is a
number that is computed by adding up all the octets in the datagram
(more or less - see the TCP spec). The result is put in the header.
TCP at the other end computes the checksum again. If they disagree,
then something bad happened to the datagram in transmission, and it is
thrown away. So here's what the datagram looks like now.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgment Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data | |U|A|P|R|S|F| |
| Offset| Reserved |R|C|S|S|Y|I| Window |
| | |G|K|H|T|N|N| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | Urgent Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| your data ... next 500 octets |
| ...... |
If we abbreviate the TCP header as "T", the whole file now looks like
this:
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T.... T.... T.... T.... T.... T.... T....
You will note that there are items in the header that I have not
described above. They are generally involved with managing the
connection. In order to make sure the datagram has arrived at its
destination, the recipient has to send back an "acknowledgement".
This is a datagram whose "Acknowledgement number" field is filled in.
For example, sending a packet with an acknowledgement of 1500
indicates that you have received all the data up to octet number 1500.
If the sender doesn't get an acknowledgement within a reasonable
amount of time, it sends the data again. The window is used to
control how much data can be in transit at any one time. It is not
practical to wait for each datagram to be acknowledged before sending
the next one. That would slow things down too much. On the other
hand, you can't just keep sending, or a fast computer might overrun
the capacity of a slow one to absorb data. Thus each end indicates
how much new data it is currently prepared to absorb by putting the
number of octets in its "Window" field. As the computer receives
data, the amount of space left in its window decreases. When it goes
to zero, the sender has to stop. As the receiver processes the data,
it increases its window, indicating that it is ready to accept more
data. Often the same datagram can be used to acknowledge receipt of a
set of data and to give permission for additional new data (by an
updated window). The "Urgent" field allows one end to tell the other
to skip ahead in its processing to a particular octet. This is often
useful for handling asynchronous events, for example when you type a
control character or other command that interrupts output. The other
fields are beyond the scope of this document.
1.1.5. The IP level
TCP sends each of these datagrams to IP. Of course it has to tell IP
the Internet address of the computer at the other end. Note that this
is all IP is concerned about. It doesn't care about what is in the
datagram, or even in the TCP header. IP's job is simply to find a
route for the datagram and get it to the other end. In order to allow
gateways or other intermediate systems to forward the datagram, it
adds its own header. The main things in this header are the source
and destination Internet address (32-bit addresses, like 128.6.4.194),
the protocol number, and another checksum. The source Internet
address is simply the address of your machine. (This is necessary so
the other end knows where the datagram came from.) The destination
Internet address is the address of the other machine. (This is
necessary so any gateways in the middle know where you want the
datagram to go.) The protocol number tells IP at the other end to
send the datagram to TCP. Although most IP traffic uses TCP, there
are other protocols that can use IP, so you have to tell IP which
protocol to send the datagram to. Finally, the checksum allows IP at
the other end to verify that the header wasn't damaged in transit.
Note that TCP and IP have separate checksums. IP needs to be able to
verify that the header didn't get damaged in transit, or it could send a
message to the wrong place. For reasons not worth discussing here, it
is both more efficient and safer to have TCP compute a separate
checksum for the TCP header and data. Once IP has tacked on its
- 13 -
header, here's what the message looks like:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TCP header, then your data ...... |
| |
If we represent the IP header by an "I", your file now looks like
this:
IT.... IT.... IT.... IT.... IT.... IT.... IT....
Again, the header contains some additional fields that have not been
discussed. Most of them are beyond the scope of this document. The
flags and fragment offset are used to keep track of the pieces when a
datagram has to be split up. This can happen when datagrams are
forwarded through a network for which they are too big. (This will be
discussed a bit more below.) The time to live is a number that is
decremented whenever the datagram passes through a system. When it
goes to zero, the datagram is discarded. This is done in case a loop
develops in the system somehow. Of course this should be impossible,
but well-designed networks are built to cope with "impossible"
conditions.
At this point, it's possible that no more headers are needed. If your
computer happens to have a direct phone line connecting it to the
destination computer, or to a gateway, it may simply send the
datagrams out on the line (though likely a synchronous protocol such
as HDLC would be used, and it would add at least a few octets at the
beginning and end).
1.1.6. The Ethernet level
However most of our networks these days use Ethernet. So now we have
to describe Ethernet's headers. Unfortunately, Ethernet has its own
addresses. The people who designed Ethernet wanted to make sure that
no two machines would end up with the same Ethernet address.
Furthermore, they didn't want the user to have to worry about
assigning addresses. So each Ethernet controller comes with an
address builtin from the factory. In order to make sure that they
would never have to reuse addresses, the Ethernet designers allocated
48 bits for the Ethernet address. People who make Ethernet equipment
have to register with a central authority, to make sure that the
numbers they assign don't overlap any other manufacturer. Ethernet is a
"broadcast medium". That is, it is in effect like an old party line
- 14 -
telephone. When you send a packet out on the Ethernet, every machine
on the network sees the packet. So something is needed to make sure
that the right machine gets it. As you might guess, this involves the
Ethernet header. Every Ethernet packet has a 14-octet header that
includes the source and destination Ethernet address, and a type code.
Each machine is supposed to pay attention only to packets with its own
Ethernet address in the destination field. (It's perfectly possible
to cheat, which is one reason that Ethernet communications are not
terribly secure.) Note that there is no connection between the
Ethernet address and the Internet address. Each machine has to have a
table of what Ethernet address corresponds to what Internet address.
(We will describe how this table is constructed a bit later.) In
addition to the addresses, the header contains a type code. The type
code is to allow for several different protocol families to be used on
the same network. So you can use TCP/IP, DECnet, Xerox NS, etc. at
the same time. Each of them will put a different value in the type
field. Finally, there is a checksum. The Ethernet controller
computes a checksum of the entire packet. When the other end receives
the packet, it recomputes the checksum, and throws the packet away if
the answer disagrees with the original. The checksum is put on the
end of the packet, not in the header. The final result is that your
message looks like this:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet destination address (first 32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet dest (last 16 bits) |Ethernet source (first 16 bits)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet source address (last 32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP header, then TCP header, then your data |
| |
...
| |
| end of your data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethernet Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If we represent the Ethernet header with "E", and the Ethernet
checksum with "C", your file now looks like this:
EIT....C EIT....C EIT....C EIT....C EIT....C
When these packets are received by the other end, of course all the
headers are removed. The Ethernet interface removes the Ethernet
header and the checksum. It looks at the type code. Since the type
code is the one assigned to IP, the Ethernet device driver passes the
datagram up to IP. IP removes the IP header. It looks at the IP
protocol field. Since the protocol type is TCP, it passes the
datagram up to TCP. TCP now looks at the sequence number. It uses
the sequence numbers and other information to combine all the
- 15 -
datagrams into the original file.
The ends our initial summary of TCP/IP. There are still some crucial
concepts we haven't gotten to, so we'll now go back and add details in
several areas. (For detailed descriptions of the items discussed here
see, RFC 793 for TCP, RFC 791 for IP, and RFC's 894 and 826 for
sending IP over Ethernet.)
1.1.7. Well-known sockets and the applications layer
So far, we have described how a stream of data is broken up into
datagrams, sent to another computer, and put back together. However
something more is needed in order to accomplish anything useful.
There has to be a way for you to open a connection to a specified
computer, log into it, tell it what file you want, and control the
transmission of the file. (If you have a different application in
mind, e.g. computer mail, some analogous protocol is needed.) This is
done by "application protocols". The application protocols run "on
top" of TCP/IP. That is, when they want to send a message, they give
the message to TCP. TCP makes sure it gets delivered to the other
end. Because TCP and IP take care of all the networking details, the
applications protocols can treat a network connection as if it were a
simple byte stream, like a terminal or phone line.
Before going into more details about applications programs, we have to
describe how you find an application. Suppose you want to send a file
to a computer whose Internet address is 128.6.4.7. To start the
process, you need more than just the Internet address. You have to
connect to the FTP server at the other end. In general, network
programs are specialized for a specific set of tasks. Most systems
have separate programs to handle file transfers, remote terminal
logins, mail, etc. When you connect to 128.6.4.7, you have to specify
that you want to talk to the FTP server. This is done by having
"well-known sockets" for each server. Recall that TCP uses port
numbers to keep track of individual conversations. User programs
normally use more or less random port numbers. However specific port
numbers are assigned to the programs that sit waiting for requests.
For example, if you want to send a file, you will start a program
called "ftp". It will open a connection using some random number, say
1234, for the port number on its end. However it will specify port
number 21 for the other end. This is the official port number for the
FTP server. Note that there are two different programs involved. You
run ftp on your side. This is a program designed to accept commands
from your terminal and pass them on to the other end. The program
that you talk to on the other machine is the FTP server. It is
designed to accept commands from the network connection, rather than
an interactive terminal. There is no need for your program to use a
well-known socket number for itself. Nobody is trying to find it.
However the servers have to have well-known numbers, so that people
can open connections to them and start sending them commands. The
official port numbers for each program are given in "Assigned
Numbers".
Note that a connection is actually described by a set of 4 numbers:
- 16 -
the Internet address at each end, and the TCP port number at each end.
Every datagram has all four of those numbers in it. (The Internet
addresses are in the IP header, and the TCP port numbers are in the
TCP header.) In order to keep things straight, no two connections can
have the same set of numbers. However it is enough for any one number
to be different. For example, it is perfectly possible for two
different users on a machine to be sending files to the same other
machine. This could result in connections with the following
parameters:
Internet addresses TCP ports
connection 1 128.6.4.194, 128.6.4.7 1234, 21
connection 2 128.6.4.194, 128.6.4.7 1235, 21
Since the same machines are involved, the Internet addresses are the
same. Since they are both doing file transfers, one end of the
connection involves the well-known port number for FTP. The only
thing that differs is the port number for the program that the users
are running. That's enough of a difference. Generally, at least one
end of the connection asks the network software to assign it a port
number that is guaranteed to be unique. Normally, it's the user's
end, since the server has to use a well-known number.
Now that we know how to open connections, let's get back to the
applications programs. As mentioned earlier, once TCP has opened a
connection, we have something that might as well be a simple wire.
All the hard parts are handled by TCP and IP. However we still need
some agreement as to what we send over this connection. In effect
this is simply an agreement on what set of commands the application
will understand, and the format in which they are to be sent.
Generally, what is sent is a combination of commands and data. They
use context to differentiate. For example, the mail protocol works
like this: Your mail program opens a connection to the mail server at
the other end. Your program gives it your machine's name, the sender
of the message, and the recipients you want it sent to. It then sends a
command saying that it is starting the message. At that point, the
other end stops treating what it sees as commands, and starts
accepting the message. Your end then starts sending the text of the
message. At the end of the message, a special mark is sent (a dot in
the first column). After that, both ends understand that your program
is again sending commands. This is the simplest way to do things, and
the one that most applications use.
File transfer is somewhat more complex. The file transfer protocol
involves two different connections. It starts out just like mail.
The user's program sends commands like "log me in as this user", "here
is my password", "send me the file with this name". However once the
command to send data is sent, a second connection is opened for the
data itself. It would certainly be possible to send the data on the
same connection, as mail does. However file transfers often take a
long time. The designers of the file transfer protocol wanted to
allow the user to continue issuing commands while the transfer is
going on. For example, the user might make an inquiry, or he might
abort the transfer. Thus the designers felt it was best to use a
- 17 -
separate connection for the data and leave the original command
connection for commands. (It is also possible to open command
connections to two different computers, and tell them to send a file
from one to the other. In that case, the data couldn't go over the
command connection.)
Remote terminal connections use another mechanism still. For remote
logins, there is just one connection. It normally sends data. When
it is necessary to send a command (e.g. to set the terminal type or to
change some mode), a special character is used to indicate that the
next character is a command. If the user happens to type that special
character as data, two of them are sent.
We are not going to describe the application protocols in detail in
this document. It's better to read the RFC's yourself. However there
are a couple of common conventions used by applications that will be
described here. First, the common network representation: TCP/IP is
intended to be usable on any computer. Unfortunately, not all
computers agree on how data is represented. There are differences in
character codes (ASCII vs. EBCDIC), in end of line conventions
(carriage return, line feed, or a representation using counts), and in
whether terminals expect characters to be sent individually or a line
at a time. In order to allow computers of different kinds to
communicate, each applications protocol defines a standard
representation. Note that TCP and IP do not care about the
representation. TCP simply sends octets. However the programs at
both ends have to agree on how the octets are to be interpreted. The
RFC for each application specifies the standard representation for
that application. Normally it is "net ASCII". This uses ASCII
characters, with end of line denoted by a carriage return followed by a
line feed. For remote login, there is also a definition of a
"standard terminal", which turns out to be a half-duplex terminal with
echoing happening on the local machine. Most applications also make
provisions for the two computers to agree on other representations
that they may find more convenient. For example, PDP-10's have 36-bit
words. There is a way that two PDP-10's can agree to send a 36-bit
binary file. Similarly, two systems that prefer full-duplex terminal
conversations can agree on that. However each application has a
standard representation, which every machine must support.
1.1.8. An example application: SMTP
In order to give a bit better idea what is involved in the application
protocols, I'm going to show an example of SMTP, which is the mail
protocol. (SMTP is "simple mail transfer protocol.) We assume that a
computer called TOPAZ.RUTGERS.EDU wants to send the following message.
Date: Sat, 27 Jun 87 13:26:31 EDT
From: hedrick@topaz.rutgers.edu
To: levy@red.rutgers.edu
Subject: meeting
Let's get together Monday at 1pm.
- 18 -
First, note that the format of the message itself is described by an
Internet standard (RFC 822). The standard specifies the fact that the
message must be transmitted as net ASCII (i.e. it must be ASCII, with
carriage return/linefeed to delimit lines). It also describes the
general structure, as a group of header lines, then a blank line, and
then the body of the message. Finally, it describes the syntax of the
header lines in detail. Generally they consist of a keyword and then a
value.
Note that the addressee is indicated as LEVY@RED.RUTGERS.EDU.
Initially, addresses were simply "person at machine". However recent
standards have made things more flexible. There are now provisions
for systems to handle other systems' mail. This can allow automatic
forwarding on behalf of computers not connected to the Internet. It
can be used to direct mail for a number of systems to one central mail
server. Indeed there is no requirement that an actual computer by the
name of RED.RUTGERS.EDU even exist. The name servers could be set up
so that you mail to department names, and each department's mail is
routed automatically to an appropriate computer. It is also possible
that the part before the @ is something other than a user name. It is
possible for programs to be set up to process mail. There are also
provisions to handle mailing lists, and generic names such as
"postmaster" or "operator".
The way the message is to be sent to another system is described by
RFC's 821 and 974. The program that is going to be doing the sending
asks the name server several queries to determine where to route the
message. The first query is to find out which machines handle mail
for the name RED.RUTGERS.EDU. In this case, the server replies that
RED.RUTGERS.EDU handles its own mail. The program then asks for the
address of RED.RUTGERS.EDU, which is 128.6.4.2. Then the mail program
opens a TCP connection to port 25 on 128.6.4.2. Port 25 is the
well-known socket used for receiving mail. Once this connection is
established, the mail program starts sending commands. Here is a
typical conversation. Each line is labelled as to whether it is from
TOPAZ or RED. Note that TOPAZ initiated the connection:
RED 220 RED.RUTGERS.EDU SMTP Service at 29 Jun 87 05:17:18
EDT
TOPAZ HELO topaz.rutgers.edu
RED 250 RED.RUTGERS.EDU - Hello, TOPAZ.RUTGERS.EDU
TOPAZ MAIL From:<hedrick@topaz.rutgers.edu>
RED 250 MAIL accepted
TOPAZ RCPT To:<levy@red.rutgers.edu>
RED 250 Recipient accepted
TOPAZ DATA
RED 354 Start mail input; end with <CRLF>.<CRLF>
TOPAZ Date: Sat, 27 Jun 87 13:26:31 EDT
TOPAZ From: hedrick@topaz.rutgers.edu
TOPAZ To: levy@red.rutgers.edu
TOPAZ Subject: meeting
TOPAZ
TOPAZ Let's get together Monday at 1pm.
TOPAZ .
- 19 -
RED 250 OK
TOPAZ QUIT
RED 221 RED.RUTGERS.EDU Service closing transmission channel
First, note that commands all use normal text. This is typical of the
Internet standards. Many of the protocols use standard ASCII
commands. This makes it easy to watch what is going on and to
diagnose problems. For example, the mail program keeps a log of each
conversation. If something goes wrong, the log file can simply be
mailed to the postmaster. Since it is normal text, he can see what
was going on. It also allows a human to interact directly with the
mail server, for testing. (Some newer protocols are complex enough
that this is not practical. The commands would have to have a syntax
that would require a significant parser. Thus there is a tendency for
newer protocols to use binary formats. Generally they are structured
like C or Pascal record structures.) Second, note that the responses
all begin with numbers. This is also typical of Internet protocols.
The allowable responses are defined in the protocol. The numbers
allow the user program to respond unambiguously. The rest of the
response is text, which is normally for use by any human who may be
watching or looking at a log. It has no effect on the operation of
the programs. (However there is one point at which the protocol uses
part of the text of the response.) The commands themselves simply
allow the mail program on one end to tell the mail server the
information it needs to know in order to deliver the message. In this
case, the mail server could get the information by looking at the
message itself. But for more complex cases, that would not be safe.
Every session must begin with a HELO, which gives the name of the
system that initiated the connection. Then the sender and recipients
are specified. (There can be more than one RCPT command, if there are
several recipients.) Finally the data itself is sent. Note that the
text of the message is terminated by a line containing just a period.
(If such a line appears in the message, the period is doubled.) After
the message is accepted, the sender can send another message, or
terminate the session as in the example above.
Generally, there is a pattern to the response numbers. The protocol
defines the specific set of responses that can be sent as answers to
any given command. However programs that don't want to analyze them
in detail can just look at the first digit. In general, responses
that begin with a 2 indicate success. Those that begin with 3
indicate that some further action is needed, as shown above. 4 and 5
indicate errors. 4 is a "temporary" error, such as a disk filling.
The message should be saved, and tried again later. 5 is a permanent
error, such as a non-existent recipient. The message should be
returned to the sender with an error message.
(For more details about the protocols mentioned in this section, see
RFC's 821/822 for mail, RFC 959 for file transfer, and RFC's 854/855
for remote logins. For the well-known port numbers, see the current
edition of Assigned Numbers, and possibly RFC 814.)
- 20 -
1.2. Protocols other than TCP: UDP and ICMP
So far, we have described only connections that use TCP. Recall that
TCP is responsible for breaking up messages into datagrams, and
reassembling them properly. However in many applications, we have
messages that will always fit in a single datagram. An example is
name lookup. When a user attempts to make a connection to another
system, he will generally specify the system by name, rather than
Internet address. His system has to translate that name to an address
before it can do anything. Generally, only a few systems have the
database used to translate names to addresses. So the user's system
will want to send a query to one of the systems that has the database.
This query is going to be very short. It will certainly fit in one
datagram. So will the answer. Thus it seems silly to use TCP. Of
course TCP does more than just break things up into datagrams. It
also makes sure that the data arrives, resending datagrams where
necessary. But for a question that fits in a single datagram, we
don't need all the complexity of TCP to do this. If we don't get an
answer after a few seconds, we can just ask again. For applications
like this, there are alternatives to TCP.
The most common alternative is UDP ("user datagram protocol"). UDP is
designed for applications where you don't need to put sequences of
datagrams together. It fits into the system much like TCP. There is a
UDP header. The network software puts the UDP header on the front of
your data, just as it would put a TCP header on the front of your data.
Then UDP sends the data to IP, which adds the IP header, putting
UDP's protocol number in the protocol field instead of TCP's protocol
number. However UDP doesn't do as much as TCP does. It doesn't
split data into multiple datagrams. It doesn't keep track of what it
has sent so it can resend if necessary. About all that UDP provides
is port numbers, so that several programs can use UDP at once. UDP
port numbers are used just like TCP port numbers. There are well-
known port numbers for servers that use UDP. Note that the UDP header
is shorter than a TCP header. It still has source and destination
port numbers, and a checksum, but that's about it. No sequence
number, since it is not needed. UDP is used by the protocols that han-
dle name lookups (see IEN 116, RFC 882, and RFC 883), and a number of
similar protocols.
Another alternative protocol is ICMP ("Internet control message
protocol"). ICMP is used for error messages, and other messages
intended for the TCP/IP software itself, rather than any particular
user program. For example, if you attempt to connect to a host, your
system may get back an ICMP message saying "host unreachable". ICMP
can also be used to find out some information about the network. See
RFC 792 for details of ICMP. ICMP is similar to UDP, in that it
handles messages that fit in one datagram. However it is even simpler
than UDP. It doesn't even have port numbers in its header. Since all
ICMP messages are interpreted by the network software itself, no port
numbers are needed to say where a ICMP message is supposed to go.
- 21 -
1.3. Keeping track of names and information: the domain system
As we indicated earlier, the network software generally needs a 32-bit
Internet address in order to open a connection or send a datagram.
However users prefer to deal with computer names rather than numbers.
Thus there is a database that allows the software to look up a name
and find the corresponding number. When the Internet was small, this
was easy. Each system would have a file that listed all of the other
systems, giving both their name and number. There are now too many
computers for this approach to be practical. Thus these files have
been replaced by a set of name servers that keep track of host names
and the corresponding Internet addresses. (In fact these servers are
somewhat more general than that. This is just one kind of information
stored in the domain system.) Note that a set of interlocking servers
are used, rather than a single central one. There are now so many
different institutions connected to the Internet that it would be
impractical for them to notify a central authority whenever they
installed or moved a computer. Thus naming authority is delegated to
individual institutions. The name servers form a tree, corresponding
to institutional structure. The names themselves follow a similar
structure. A typical example is the name BORAX.LCS.MIT.EDU. This is a
computer at the Laboratory for Computer Science (LCS) at MIT. In
order to find its Internet address, you might potentially have to
consult 4 different servers. First, you would ask a central server
(called the root) where the EDU server is. EDU is a server that keeps
track of educational institutions. The root server would give you the
names and Internet addresses of several servers for EDU. (There are
several servers at each level, to allow for the possibly that one
might be down.) You would then ask EDU where the server for MIT is.
Again, it would give you names and Internet addresses of several
servers for MIT. Generally, not all of those servers would be at MIT,
to allow for the possibility of a general power failure at MIT. Then
you would ask MIT where the server for LCS is, and finally you would
ask one of the LCS servers about BORAX. The final result would be the
Internet address for BORAX.LCS.MIT.EDU. Each of these levels is
referred to as a "domain". The entire name, BORAX.LCS.MIT.EDU, is
called a "domain name". (So are the names of the higher-level
domains, such as LCS.MIT.EDU, MIT.EDU, and EDU.)
Fortunately, you don't really have to go through all of this most of
the time. First of all, the root name servers also happen to be the
name servers for the top-level domains such as EDU. Thus a single
query to a root server will get you to MIT. Second, software
generally remembers answers that it got before. So once we look up a
name at LCS.MIT.EDU, our software remembers where to find servers for
LCS.MIT.EDU, MIT.EDU, and EDU. It also remembers the translation of
BORAX.LCS.MIT.EDU. Each of these pieces of information has a "time to
live" associated with it. Typically this is a few days. After that,
the information expires and has to be looked up again. This allows
institutions to change things.
The domain system is not limited to finding out Internet addresses.
Each domain name is a node in a database. The node can have records
that define a number of different properties. Examples are Internet
- 22 -
address, computer type, and a list of services provided by a computer.
A program can ask for a specific piece of information, or all
information about a given name. It is possible for a node in the
database to be marked as an "alias" (or nickname) for another node.
It is also possible to use the domain system to store information
about users, mailing lists, or other objects.
There is an Internet standard defining the operation of these
databases, as well as the protocols used to make queries of them.
Every network utility has to be able to make such queries, since this
is now the official way to evaluate host names. Generally utilities
will talk to a server on their own system. This server will take care
of contacting the other servers for them. This keeps down the amount
of code that has to be in each application program.
The domain system is particularly important for handling computer
mail. There are entry types to define what computer handles mail for a
given name, to specify where an individual is to receive mail, and to
define mailing lists.
(See RFC's 882, 883, and 973 for specifications of the domain system.
RFC 974 defines the use of the domain system in sending mail.)
1.4. Routing
The description above indicated that the IP implementation is
responsible for getting datagrams to the destination indicated by the
destination address, but little was said about how this would be done.
The task of finding how to get a datagram to its destination is
referred to as "routing". In fact many of the details depend upon the
particular implementation. However some general things can be said.
First, it is necessary to understand the model on which IP is based.
IP assumes that a system is attached to some local network. We assume
that the system can send datagrams to any other system on its own
network. (In the case of Ethernet, it simply finds the Ethernet
address of the destination system, and puts the datagram out on the
Ethernet.) The problem comes when a system is asked to send a
datagram to a system on a different network. This problem is handled
by gateways. A gateway is a system that connects a network with one
or more other networks. Gateways are often normal computers that
happen to have more than one network interface. For example, we have a
Unix machine that has two different Ethernet interfaces. Thus it is
connected to networks 128.6.4 and 128.6.3. This machine can act as a
gateway between those two networks. The software on that machine must
be set up so that it will forward datagrams from one network to the
other. That is, if a machine on network 128.6.4 sends a datagram to
the gateway, and the datagram is addressed to a machine on network
128.6.3, the gateway will forward the datagram to the destination.
Major communications centers often have gateways that connect a number
of different networks. (In many cases, special-purpose gateway
systems provide better performance or reliability than general-purpose
systems acting as gateways. A number of vendors sell such systems.)
- 23 -
Routing in IP is based entirely upon the network number of the
destination address. Each computer has a table of network numbers.
For each network number, a gateway is listed. This is the gateway to
be used to get to that network. Note that the gateway doesn't have to
connect directly to the network. It just has to be the best place to
go to get there. For example at Rutgers, our interface to NSFnet is
at the John von Neuman Supercomputer Center (JvNC). Our connection to
JvNC is via a high-speed serial line connected to a gateway whose
address is 128.6.3.12. Systems on net 128.6.3 will list 128.6.3.12 as
the gateway for many off-campus networks. However systems on net
128.6.4 will list 128.6.4.1 as the gateway to those same off-campus
networks. 128.6.4.1 is the gateway between networks 128.6.4 and
128.6.3, so it is the first step in getting to JvNC.
When a computer wants to send a datagram, it first checks to see if
the destination address is on the system's own local network. If so,
the datagram can be sent directly. Otherwise, the system expects to
find an entry for the network that the destination address is on. The
datagram is sent to the gateway listed in that entry. This table can
get quite big. For example, the Internet now includes several hundred
individual networks. Thus various strategies have been developed to
reduce the size of the routing table. One strategy is to depend upon
"default routes". Often, there is only one gateway out of a network.
This gateway might connect a local Ethernet to a campus-wide backbone
network. In that case, we don't need to have a separate entry for
every network in the world. We simply define that gateway as a
"default". When no specific route is found for a datagram, the
datagram is sent to the default gateway. A default gateway can even
be used when there are several gateways on a network. There are
provisions for gateways to send a message saying "I'm not the best
gateway -- use this one instead." (The message is sent via ICMP. See
RFC 792.) Most network software is designed to use these messages to
add entries to their routing tables. Suppose network 128.6.4 has two
gateways, 128.6.4.59 and 128.6.4.1. 128.6.4.59 leads to several other
internal Rutgers networks. 128.6.4.1 leads indirectly to the NSFnet.
Suppose we set 128.6.4.59 as a default gateway, and have no other
routing table entries. Now what happens when we need to send a
datagram to MIT? MIT is network 18. Since we have no entry for
network 18, the datagram will be sent to the default, 128.6.4.59. As
it happens, this gateway is the wrong one. So it will forward the
datagram to 128.6.4.1. But it will also send back an error saying in
effect: "to get to network 18, use 128.6.4.1". Our software will then
add an entry to the routing table. Any future datagrams to MIT will
then go directly to 128.6.4.1. (The error message is sent using the
ICMP protocol. The message type is called "ICMP redirect.")
Most IP experts recommend that individual computers should not try to
keep track of the entire network. Instead, they should start with
default gateways, and let the gateways tell them the routes, as just
described. However this doesn't say how the gateways should find out
about the routes. The gateways can't depend upon this strategy. They
have to have fairly complete routing tables. For this, some sort of
routing protocol is needed. A routing protocol is simply a technique
for the gateways to find each other, and keep up to date about the
- 24 -
best way to get to every network. RFC 1009 contains a review of
gateway design and routing. However rip.doc is probably a better
introduction to the subject. It contains some tutorial material, and a
detailed description of the most commonly-used routing protocol.
1.5. Details about Internet addresses: subnets and broadcasting
As indicated earlier, Internet addresses are 32-bit numbers, normally
written as 4 octets (in decimal), e.g. 128.6.4.7. There are actually 3
different types of address. The problem is that the address has to
indicate both the network and the host within the network. It was
felt that eventually there would be lots of networks. Many of them
would be small, but probably 24 bits would be needed to represent all
the IP networks. It was also felt that some very big networks might
need 24 bits to represent all of their hosts. This would seem to lead
to 48 bit addresses. But the designers really wanted to use 32 bit
addresses. So they adopted a kludge. The assumption is that most of
the networks will be small. So they set up three different ranges of
address. Addresses beginning with 1 to 126 use only the first octet
for the network number. The other three octets are available for the
host number. Thus 24 bits are available for hosts. These numbers are
used for large networks. But there can only be 126 of these very big
networks. The Arpanet is one, and there are a few large commercial
networks. But few normal organizations get one of these "class A"
addresses. For normal large organizations, "class B" addresses are
used. Class B addresses use the first two octets for the network
number. Thus network numbers are 128.1 through 191.254. (We avoid 0
and 255, for reasons that we see below. We also avoid addresses
beginning with 127, because that is used by some systems for special
purposes.) The last two octets are available for host addesses,
giving 16 bits of host address. This allows for 64516 computers,
which should be enough for most organizations. (It is possible to get
more than one class B address, if you run out.) Finally, class C
addresses use three octets, in the range 192.1.1 to 223.254.254.
These allow only 254 hosts on each network, but there can be lots of
these networks. Addresses above 223 are reserved for future use, as
class D and E (which are currently not defined).
Many large organizations find it convenient to divide their network
number into "subnets". For example, Rutgers has been assigned a class B
address, 128.6. We find it convenient to use the third octet of the
address to indicate which Ethernet a host is on. This division has no
significance outside of Rutgers. A computer at another institution
would treat all datagrams addressed to 128.6 the same way. They would
not look at the third octet of the address. Thus computers outside
Rutgers would not have different routes for 128.6.4 or 128.6.5. But
inside Rutgers, we treat 128.6.4 and 128.6.5 as separate networks. In
effect, gateways inside Rutgers have separate entries for each Rutgers
subnet, whereas gateways outside Rutgers just have one entry for
128.6. Note that we could do exactly the same thing by using a
separate class C address for each Ethernet. As far as Rutgers is
concerned, it would be just as convenient for us to have a number of
class C addresses. However using class C addresses would make things
inconvenient for the rest of the world. Every institution that wanted
- 25 -
to talk to us would have to have a separate entry for each one of our
networks. If every institution did this, there would be far too many
networks for any reasonable gateway to keep track of. By subdividing a
class B network, we hide our internal structure from everyone else, and
save them trouble. This subnet strategy requires special provi-
sions in the network software. It is described in RFC 950.
0 and 255 have special meanings. 0 is reserved for machines that
don't know their address. In certain circumstances it is possible for a
machine not to know the number of the network it is on, or even its own
host address. For example, 0.0.0.23 would be a machine that knew it
was host number 23, but didn't know on what network.
255 is used for "broadcast". A broadcast is a message that you want
every system on the network to see. Broadcasts are used in some
situations where you don't know who to talk to. For example, suppose
you need to look up a host name and get its Internet address.
Sometimes you don't know the address of the nearest name server. In
that case, you might send the request as a broadcast. There are also
cases where a number of systems are interested in information. It is
then less expensive to send a single broadcast than to send datagrams
individually to each host that is interested in the information. In
order to send a broadcast, you use an address that is made by using
your network address, with all ones in the part of the address where
the host number goes. For example, if you are on network 128.6.4, you
would use 128.6.4.255 for broadcasts. How this is actually
implemented depends upon the medium. It is not possible to send
broadcasts on the Arpanet, or on point to point lines. However it is
possible on an Ethernet. If you use an Ethernet address with all its
bits on (all ones), every machine on the Ethernet is supposed to look
at that datagram.
Although the official broadcast address for network 128.6.4 is now
128.6.4.255, there are some other addresses that may be treated as
broadcasts by certain implementations. For convenience, the standard
also allows 255.255.255.255 to be used. This refers to all hosts on
the local network. It is often simpler to use 255.255.255.255 instead
of finding out the network number for the local network and forming a
broadcast address such as 128.6.4.255. In addition, certain older
implementations may use 0 instead of 255 to form the broadcast
address. Such implementations would use 128.6.4.0 instead of
128.6.4.255 as the broadcast address on network 128.6.4. Finally,
certain older implementations may not understand about subnets. Thus
they consider the network number to be 128.6. In that case, they will
assume a broadcast address of 128.6.255.255 or 128.6.0.0. Until
support for broadcasts is implemented properly, it can be a somewhat
dangerous feature to use.
Because 0 and 255 are used for unknown and broadcast addresses, normal
hosts should never be given addresses containing 0 or 255. Addresses
should never begin with 0, 127, or any number above 223. Addresses
violating these rules are sometimes referred to as "Martians", because
of rumors that the Central University of Mars is using network 225.
- 26 -
1.6. Datagram fragmentation and reassembly
TCP/IP is designed for use with many different kinds of network.
Unfortunately, network designers do not agree about how big packets
can be. Ethernet packets can be 1500 octets long. Arpanet packets
have a maximum of around 1000 octets. Some very fast networks have
much larger packet sizes. At first, you might think that IP should
simply settle on the smallest possible size. Unfortunately, this
would cause serious performance problems. When transferring large
files, big packets are far more efficient than small ones. So we want
to be able to use the largest packet size possible. But we also want
to be able to handle networks with small limits. There are two
provisions for this. First, TCP has the ability to "negotiate" about
datagram size. When a TCP connection first opens, both ends can send
the maximum datagram size they can handle. The smaller of these
numbers is used for the rest of the connection. This allows two
implementations that can handle big datagrams to use them, but also
lets them talk to implementations that can't handle them. However
this doesn't completely solve the problem. The most serious problem
is that the two ends don't necessarily know about all of the steps in
between. For example, when sending data between Rutgers and Berkeley,
it is likely that both computers will be on Ethernets. Thus they will
both be prepared to handle 1500-octet datagrams. However the
connection will at some point end up going over the Arpanet. It can't
handle packets of that size. For this reason, there are provisions to
split datagrams up into pieces. (This is referred to as
"fragmentation".) The IP header contains fields indicating the a
datagram has been split, and enough information to let the pieces be
put back together. If a gateway connects an Ethernet to the Arpanet,
it must be prepared to take 1500-octet Ethernet packets and split them
into pieces that will fit on the Arpanet. Furthermore, every host
implementation of TCP/IP must be prepared to accept pieces and put
them back together. This is referred to as "reassembly".
TCP/IP implementations differ in the approach they take to deciding on
datagram size. It is fairly common for implementations to use
576-byte datagrams whenever they can't verify that the entire path is
able to handle larger packets. This rather conservative strategy is
used because of the number of implementations with bugs in the code to
reassemble fragments. Implementors often try to avoid ever having
fragmentation occur. Different implementors take different approaches
to deciding when it is safe to use large datagrams. Some use them
only for the local network. Others will use them for any network on
the same campus. 576 bytes is a "safe" size, which every
implementation must support.
1.7. Ethernet encapsulation: ARP
There was a brief discussion earlier about what IP datagrams look like
on an Ethernet. The discussion showed the Ethernet header and
checksum. However it left one hole: It didn't say how to figure out
what Ethernet address to use when you want to talk to a given Internet
address. In fact, there is a separate protocol for this, called ARP
("address resolution protocol"). (Note by the way that ARP is not an
- 27 -
IP protocol. That is, the ARP datagrams do not have IP headers.)
Suppose you are on system 128.6.4.194 and you want to connect to
system 128.6.4.7. Your system will first verify that 128.6.4.7 is on
the same network, so it can talk directly via Ethernet. Then it will
look up 128.6.4.7 in its ARP table, to see if it already knows the
Ethernet address. If so, it will stick on an Ethernet header, and
send the packet. But suppose this system is not in the ARP table.
There is no way to send the packet, because you need the Ethernet
address. So it uses the ARP protocol to send an ARP request.
Essentially an ARP request says "I need the Ethernet address for
128.6.4.7". Every system listens to ARP requests. When a system sees
an ARP request for itself, it is required to respond. So 128.6.4.7
will see the request, and will respond with an ARP reply saying in
effect "128.6.4.7 is 8:0:20:1:56:34". (Recall that Ethernet addresses
are 48 bits. This is 6 octets. Ethernet addresses are conventionally
shown in hex, using the punctuation shown.) Your system will save
this information in its ARP table, so future packets will go directly.
Most systems treat the ARP table as a cache, and clear entries in it
if they have not been used in a certain period of time.
Note by the way that ARP requests must be sent as "broadcasts". There
is no way that an ARP request can be sent directly to the right
system. After all, the whole reason for sending an ARP request is
that you don't know the Ethernet address. So an Ethernet address of
all ones is used, i.e. ff:ff:ff:ff:ff:ff. By convention, every
machine on the Ethernet is required to pay attention to packets with
this as an address. So every system sees every ARP requests. They
all look to see whether the request is for their own address. If so,
they respond. If not, they could just ignore it. (Some hosts will
use ARP requests to update their knowledge about other hosts on the
network, even if the request isn't for them.) Note that packets whose
IP address indicates broadcast (e.g. 255.255.255.255 or 128.6.4.255)
are also sent with an Ethernet address that is all ones.
1.8. Getting more information
This directory contains documents describing the major protocols.
There are literally hundreds of documents, so we have chosen the ones
that seem most important. Internet standards are called RFC's. RFC
stands for Request for Comment. A proposed standard is initially
issued as a proposal, and given an RFC number. When it is finally
accepted, it is added to Official Internet Protocols, but it is still
referred to by the RFC number. We have also included two IEN's.
(IEN's used to be a separate classification for more informal
documents. This classification no longer exists -- RFC's are now used
for all official Internet documents, and a mailing list is used for
more informal reports.) The convention is that whenever an RFC is
revised, the revised version gets a new number. This is fine for most
purposes, but it causes problems with two documents: Assigned Numbers
and Official Internet Protocols. These documents are being revised
all the time, so the RFC number keeps changing. You will have to look
in rfc-index.txt to find the number of the latest edition. Anyone who
is seriously interested in TCP/IP should read the RFC describing IP
(791). RFC 1009 is also useful. It is a specification for gateways
- 28 -
to be used by NSFnet. As such, it contains an overview of a lot of
the TCP/IP technology. You should probably also read the description
of at least one of the application protocols, just to get a feel for
the way things work. Mail is probably a good one (821/822). TCP
(793) is of course a very basic specification. However the spec is
fairly complex, so you should only read this when you have the time
and patience to think about it carefully. Fortunately, the author of
the major RFC's (Jon Postel) is a very good writer. The TCP RFC is
far easier to read than you would expect, given the complexity of what
it is describing. You can look at the other RFC's as you become
curious about their subject matter.
Here is a list of the documents you are more likely to want:
rfc-index list of all RFC's
rfc1012 somewhat fuller list of all RFC's
rfc1011 Official Protocols. It's useful to scan this to see
what tasks protocols have been built for. This defines
which RFC's are actual standards, as opposed to
requests for comments.
rfc1010 Assigned Numbers. If you are working with TCP/IP, you
will probably want a hardcopy of this as a reference.
It's not very exciting to read. It lists all the
offically defined well-known ports and lots of other
things.
rfc1009 NSFnet gateway specifications. A good overview of IP
routing and gateway technology.
rfc1001/2 netBIOS: networking for PC's
rfc973 update on domains
rfc959 FTP (file transfer)
rfc950 subnets
rfc937 POP2: protocol for reading mail on PC's
rfc894 how IP is to be put on Ethernet, see also rfc825
rfc882/3 domains (the database used to go from host names to
Internet address and back -- also used to handle UUCP
these days). See also rfc973
rfc854/5 telnet - protocol for remote logins
rfc826 ARP - protocol for finding out Ethernet addresses
rfc821/2 mail
- 29 -
rfc814 names and ports - general concepts behind well-known
ports
rfc793 TCP
rfc792 ICMP
rfc791 IP
rfc768 UDP
rip.doc details of the most commonly-used routing protocol
ien-116 old name server (still needed by several kinds of
system)
ien-48 the Catenet model, general description of the
philosophy behind TCP/IP
The following documents are somewhat more specialized.
rfc813 window and acknowledgement strategies in TCP
rfc815 datagram reassembly techniques
rfc816 fault isolation and resolution techniques
rfc817 modularity and efficiency in implementation
rfc879 the maximum segment size option in TCP
rfc896 congestion control
rfc827,888,904,975,985
EGP and related issues
To those of you who may be reading this document remotely instead of
at Rutgers: The most important RFC's have been collected into a
three-volume set, the DDN Protocol Handbook. It is available from the
DDN Network Information Center, SRI International, 333 Ravenswood
Avenue, Menlo Park, California 94025 (telephone: 800-235-3155). You
should be able to get them via anonymous FTP from sri-nic.arpa.
rip.doc is available by anonymous FTP from topaz.rutgers.edu, as
/pub/tcp-ip-docs/rip.doc.
IBM PC 360k floppies with ARC'ed versions of the RFC's and IEN's are
also available from the TAPR office, thanks to Andy Freeborn, N0CCZ.
1.9. Overview of the KA9Q Internet Package
The software associated with this document represents the culmination of
what might be described as a first phase of implementaton. The emphasis
to date has been on building a robust platform on which to build real
- 30 -
networks. To this end, the core protocols have been extensively tested
and verified. In addition, great emphasis has been placed on increasing
the portability of the software, supporting more and more hardware
interfaces, and making it possible to use as many networking technolo-
gies (asynch or RS-232 lines, Ethernet, various packet radio interfaces,
digipeaters, NET/ROM, etc) as possible.
The down side is that the user interface can be described at best as
"terse". The good news is that many individuals are working on improv-
ing the interface, and great strides have been made in the Macintosh
implementation. In the meantime, we ask only that you realize what our
priorities have been, and understand that even the implementors aren't
always proud of "how it looks".
This release provides support for the IP, ICMP, TCP, UDP, FTP, SMTP, and
Telnet protocols from the basic Arpanet set. In addition, the ARP pro-
tocol is available for address resolution on AX.25 and Ethernet inter-
faces, and support is provided for NET/ROM used as a transport. It is
unfortunately necessary, as a result of the ongoing NET/ROM vs TheNet
debate, to mention that the NET/ROM implementation included here is the
original work of Dan Frank, W9NK, working solely from documents pub-
lished by Software 2000.
This release includes sources that are known to compile and run well on
PC clones using MS-Dos, several flavors of System V Unix, including HP-
UX and Microport on AT clones, the HP Portable Plus, the Atari ST, and
the NEC PC-9801.
Binaries are available on floppy for the PC and clones as part of this
release. Floppies are available for the Mactintosh version, which is
maintained separately but in parallel with the mainstream release.
Other machines for which code is provided that may or may not (probably
not) work include the Amiga and BSD Unix.
- 31 -
2. Installation
2.1. What an IP Address Is, and How to Get One
IP Addresses are 32 bit numbers that uniquely identify a given machine
(or "host") running the TCP/IP protocol suite. All of the possible 32
bit numbers are coordinated by an entity known as the Network Informa-
tion Center, or NIC. Amateur Radio operators are fortunate in that a
"Class A Subnet" consisting of 24 bits of address, in the range
44.X.X.X, has been reserved for our use. By general concensus, Brian
Kantor, WB6CYT, of San Diego, CA, now serves as the top level adminis-
trator of the 44.X.X.X address space, and assigns blocks of addresses to
regional coordinators from around the world.
You need to have a unique address before you can link in with the rest
of the networked world. The best way to get one is to ask around the
local packet community and find out who your local address coordinator
is. Your local coordinator will then assign you an address from the
block for your area.
Brian Kantor can be reached as brian@ucsd.edu on the Internet if you
need help locating your local address coordinator.
2.2. Configuring a TNC for TCP/IP Operation
This section describes the procedure for configuring various packet
radio Terminal Node Controller units (TNC's) for operation with the KA9Q
package. Readers who will be using the package with only SLIP or Ether-
net (wired) connections can feel free to skip ahead to section 2.2.
There are now several choices for TNCs to be used with the TCP/IP
network code. Versions of the Keep It Simple Stupid TNC interface
software (KISS) are available for the TNC-1, the TNC-2, the VADCG board
and clones (Ashby), the Kantronics family of TNCs, and the AEA
TNCs. Following are the different setup/configuration modes for the dif-
ferent TNCs.
2.2.1. TAPR TNC-1 and Clones
The firmware for the TNC-1 is available in either a downloadable version
or a stand alone version. I will describe only the stand alone
version here. Locate the ROM labeled E000 and remove it. Insert the
KISS PROM in its place making sure that you orient the prom in the
same direction (failure to do so will result in smoked PROM). Connect
your TNC-1 to your computer using an RS-232 cable. A cable that
passes the signals from pins 2, 3, and 7 is suffi- cient.
Since the TNC-1 has no switches for setting the baud rate to the com-
puter the firmware has been "hard wired" to 4800 baud. See the docu-
mentation that comes with the TNC-1 version of KISS for instructions on
how to patch the .HEX file for other baud rates.
There is also a newer version of the TNC-1 KISS firmware that is
- 32 -
documented in the TNC_TNC1.ARC file in the distribution.
TAPR can provide programmed TNC-1 KISS EPROMs.
2.2.2. TAPR TNC-2 and Clones
The standard firmware for the TNC-2 now supports a 'KISS' command to
turn on KISS support. If you wish to use the KISS command included in
1.1.6 firmware, read your TNC documentation for more info.
If you want to run KISS only, or have an older TNC-2 without the KISS
command, dig out the TNC_TNC2.ARC package and read the docs included on
how to program an EPROM with the firmware (or buy a ROM from TAPR), and
then proceed.
Open up your TNC and locate the ROM. It is in the socket labeled "U23."
Using a small nail file or screwdriver gently pry up the existing
EPROM. Carefully press the new EPROM into place being sure that the
orientation is the same. If you are installing the 2764 type of
EPROM you will need to make a small modification to the TNC. There is a
location on the board just above the first RAM socket labeled JMP-
6. Turn the board over and cut the trace joining the two pads. Solder
a two-pin jumper header in place. When using a type 2764 the
jumper at JMP-6 should be removed and installed when a type 27256
EPROM is being used. That should complete the hardware part of the
installa- tion. As an alternative you may choose to burn the KISS code
into a 27256 and not bother with jumpers.
Attach your TNC to your PC using an RS-232C cable. You can use the same
cable that you were using to connect your PC to your TNC. If you are
doing this for the first time and are not sure about your cabling, a
cable with just pins 2, 3, and 7 passed through is sufficient. Some
PCs like to see the signals Clear To Send (CTS, pin 5), Data Set Ready
(DSR, pin 6), and Data Carrier Detect (DCD, pin 8) asserted. You
can set this up by jumpering pin 4 to 5, and pin 20 to pins 6 and 8 at
the female DB-25 connector that goes to the PC.
Now to verify that the TNC still works. Apply power to the TNC and
turn it on. The STA, CON, and PWR LEDs should come on and the STA
and CON lights should go out again about 1 second later. If you have
the type 2764 EPROM with the KISS code in it one or both of the
STA and CON LEDs will begin to flash. If the CON LED flashes you have
8Kb of RAM in the TNC. If the STA LED flashes you have 16Kb of RAM.
If both LEDs flash you have 32 Kb of RAM. The flashing of the LEDs ver-
ifies the proper operation of the TNC.
2.2.3. AEA PK-232
If you have one of these boxes, congratulations! You do not have to
change PROMS! KISS is already installed as a standard feature if you
have a recent release of the firmware, 4-MAR-87 or later for the PK-
232, or 21-JAN-87 or later for the PK-87, you have KISS in your TNC
already. To make it work first ensure that your computer can communi-
cate with the TNC in standard packet mode. This will ensure
- 33 -
that the computer, TNC, cabling, and radio are all operating properly.
[Please note that one of the commands "PACKET" is not valid on the PK-
87 and will only elicit a "Huh?" response. Please note that comments
have been added to the commands. Do not type the information following
the double dash or type the double dash itself.]
Here is the sequence of commands that will turn on the KISS mode for
the AEA products:
AWLEN 8 -- ensure it can speak 8 bit data
PARITY 0 -- no parity
RESTART -- warm reset; make commands take effect
PACKET -- PK-232 or Heath only
TONE 3 -- PK-87 only
START 0 -- disable software flow control
STOP 0
XON 0
XOFF 0
XFLOW off
CONMODE trans -- pass through all characters
HPOLL off -- disable host polling
KISS on -- enable KISS version of host mode
RAWHDLC on -- turn off AX25L2 (now handled by the PC)
PPERSIST on -- turn off DWAIT and enable p-persistence
HOST on -- start KISS running
The PK-87 or the PK-232 will remain in the KISS mode until you send a
break (~200ms of spacing) or until you send the command character three
times (^C ^C ^C) in quick succession. Beware! Some terminal emulators
(like YAPP) will send a break signal when you exit from them.
That will undo your work and cause all manner of confusion. The termi-
nal program PROCOMM seems to work just fine. The TNC may also be
switched back to ordinary AX.25 mode by issuing the following command
from within NET.EXE:
param ax0 255
AEA is rumored to be reworking their software so that entering just the
"KISS" command will do all of the above. Check your documentation to see
how your version works.
2.2.4. Kantronics TNC's
Kantronics includes KISS support in their products. It is the simplest
of the commercial implementations of KISS to configure and use.
First setup and operate your KAM, KPC-II, or KPC-4 for standard packet
operation. This will ensure that the computer, TNC, cabling, and radio
are operating properly. Use your terminal program to send the following
commands:
ABAUD 4800 -- baud rate to what you will be using when
net is running (set by the attach command)
- 34 -
DWAIT 0 -- disable DWAIT
PERSIST 50 -- enable persistence and set it to about 20%
SLOTTIME 16 -- set the slot time to 160 ms
KISS ON -- Enable KISS mode at the next reset
PERM -- make above command permanent so that KISS
will be entered whenever TNC is powered up
RESET -- start KISS
If you wish to have the the TNC revert back to ordinary AX.25 mode of
opera- tion you should omit the PERM command from the above sequence.
That way the TNC will revert back to ordinary AX.25 mode when the
power is removed and restored to the TNC. The TNC may be switched
back to ordinary AX.25 mode by issuing the command:
param ax0 255
This command will work even if the PERM command has been used to make
KISS the default mode of operation.
2.2.5. Paccomm PC-100 Card
There have been problems in the development of the driver for this card,
and though support is included in this release, it is unclear whether
the driver provided works at all, or what the proper way to configure
the PC-100 is. An individual is working on improving the driver, and we
hope to include his results soon.
2.2.6. DRSI
DRSI provides a copy of the KA9Q package configured for their card
directly. Contact DRSI about the current level of support they provide.
At some point, their driver will hopefully be integrated back into the
mainstream release.
2.3. IBM PC and Clones
2.3.1. Installing the Plug'N'Play Disk
For users of IBM PC's and Clones, we try to make life as simple as pos-
sible. There is a 360k floppy disk available from TAPR (see the appen-
dices for contact information) that is almost ready to go. You "Plug"
the disk in, edit a couple of files with your favorite text editor, and
then you're ready to "Play". Instructions on editting the files are
embedded as comments in the files, with a readme file on the disk to get
you started. For completeness, information about the files is included
here as well.
2.3.1.1. The AUTOEXEC.NET File
The AUTOEXEC.NET file (called STARTUP.NET under Unix, and other things
elsewhere) works a lot like the AUTOEXEC.BAT file in Dos, hence the
name. When NET first starts up, it reads AUTOEXEC.BAT and executes all
of the commands as if they had been typed in to the program from the
keyboard. This provides an easy mechanism for setting up the initial
- 35 -
system configuration, including setting the hostname, AX.25 parameters,
interfaces used, servers to start, and protocol variables.
The suggested procedure is to start with the AUTOEXEC.NET file included
on the plug and play disk, and go from there. If you don't have the
plug and play disk, review the command summary elsewhere in this docu-
ment, and wing it...
2.3.1.2. The FTPUSERS File
Since MS-DOS was designed as a single-user operating system, it pro-
vides no access control; all files can be read, written or deleted by
the local user. It is usually undesirable to give such open access to a
system to remote network users. The FTP server therefore provides its
own access control mechan- ism.
The file "/ftpusers" is used to control remote FTP access. The default
is NO access; if this file does not exist, the FTP server will be
unusable. A remote user must first "log in" to the system, giving a
valid name and password listed in /ftpusers, before he or she can
transfer files.
Each entry in /ftpusers consists of a single line of the form
username password path1 permissions1 path2 permissions2 ...
There must be exactly one space between each field. Comment lines are
begun with "#" in column one.
"username" is the user's login name.
"password" is the required password. Note that this is in plain-
text; therefore it is not a good idea to give general read permission
to the root directory. A password of "*" (a single asterisk) means that
any password is acceptable.
"/pathN" is an allowable prefix on accessible files. Before any file
or directory operation, the current directory and the user specified
file name are joined to form an absolute path name in "canonical" form
(i.e., a full path name starting at the root, with "./" and "../"
references, as well as redundant /'s, recognized and removed). The
result MUST begin with an allowable path prefix; if not, the opera-
tion is denied. NB! Under MS-DOS, this field must use backslashes ("/"),
NOT forward slashes ("/"). This field must always begin with a "/",
i.e., at the root directory.
"permissionsN" is a decimal number granting permission for read, create
and write operations. If the low order bit (0x1) is set, the user is
allowed to read a file subject to the path name prefix restriction. If
the next bit (0x2) is set, the user is allowed to create a
new file if it does not overwrite an existing file. If the third bit
(0x4) is set, the user is allowed to write a file even if it
overwrites an existing file, and in addi- tion he may delete files.
Again, all operations are allowed subject to the path name prefix
- 36 -
restrictions. Permissions may be combined by adding bits, for example,
0x3 (= 0x2 + 0x1) means that the user is given read and create per-
mission, but not overwrite/delete permission.
For example, suppose /ftpusers on machine "pc.ka9q.ampr" contains the
line
friendly test /testdir 7
A session using this account would look like this:
net> ftp pc.ka9q.ampr
SYN Sent
Established
250 pc.ka9q.ampr FTP version 871225.5 ready at Wed Jan 20
16:27:18 1988
user friendly
331 Enter PASS command
pass test
230 Logged in
The user now has read, write, overwrite and delete privileges for any
file under /testdir; he may not access any other files.
Here are some more sample entries in /ftpusers:
karn foobar / 7 # User "karn" password "foobar" may read,
# write, overwrite and delete any file on
# system.
guest bletch /g/bogus 3 # User "guest" password "bletch" may read
# any file under /g/bogus and its subdirs,
# and may create new files that do not
# overwrite existing files. He may NOT
# delete any files.
anonymous * /public 1 # User "anonymous" (any password) may read
# files under /public and subdir; he may
# not create, overwrite or delete any
# files.
The last entry is a standard convention for keeping a repository of
downloadable files; in particular, the username "anonymous" is an
established ARPAnet convention. Every system providing an FTP server is
encouraged to provide restricted access to an 'anonymous' user.
2.3.1.3. The HOSTS.NET File
The file HOSTS.NET provides a mapping between internet addresses and
symbolic hostnames. It is used by NET to look up a hostname to figure
out the correct IP address to use. This version of NET does not include
nameserver support (see the discussion earlier in this document), and so
uses this static file for name lookups. Tabs are recommended between
the host number and host name. Here is an example of some HOSTS.NET
- 37 -
entries:
44.96.0.2 wb2sef xt.wb2sef
44.96.0.16 n8fjb
44.96.0.17 ka3lyq
Note that the domain name .AMPR.ORG has been assigned for amateur radio.
By default, we assume that the hostname is the user's callsign in the
case where a user has one system online, and so <callsign>.AMPR.ORG is
the implied official hostname. If you have more than one machine on the
air, distinguish them by prefixing a familiar name followed by a period,
as in "winfree.n3eua" or "at.n0ccz".
Note that the use of a callsign as a host name has nothing to do with
the "mycall" parameter. It is convenient to use the callsign as a host-
name, and required to use the callsign for "mycall" to properly identify
a station according to FCC rules.
2.3.2. Installing on a Hard Disk
To install the software on a hard disk, just clone the directory struc-
ture and file layout from the floppy disk. All paths are relative to
the root directory of the current drive.
2.4. Unix
To run NET under Unix, you'll need to compile the program from sources.
To do so, unpack the source archive into a directory, edit the beginning
of makefile.unx to pick your Unix variant, edit config.h to enable the
appropriate interface hardware (slip and kiss are probably all that will
work), the run 'make -f makefile.unx'. There's nothing wrong with copy-
ing the makefile.unx file to makefile and doing the editting there...
personal preference.
The basic requirements are that the serial ports to be used by net must
have their permissions set so that they are read-write for the userid
that will run net. For example, you can define a user named 'net' and
make that user own tty000 and tty001. The protection for the ttys should
be crw------- (600). Logins must be turned off for those ports, i.e.
there must not be any other process, such as a getty or init, trying to
access them. The attach line is virtually the same as for the PC, except
that the I/O address argument is ignored and the I/O vector argument is
now the tty name. For example:
attach asy 0 /dev/tty000 ax25 ax0 2048 256 4800
attach asy 0 /dev/tty001 ax25 ax1 2048 256 4800
The Unix version of Net uses two environment variables, NETHOME and
NETSPOOL. A possible configuration might be
NETHOME=/usr/net NETSPOOL=/usr/spool
The directories needed are /usr/net, /usr/net/finger, /usr/spool/mail/,
- 38 -
and /usr/spool/mqueue. See also the documentation on the W2XO BBS
(sources and documentation are included in the NET source distribution),
as there are some important interactions if you intend to run the PBBS
code with NET under Unix.
The Unix version of NET currently supports only serial ports, with the
KISS and SLIP protocols.
2.5. Macintosh
This release does not include Macintosh code. A separate group is work-
ing on the Macintosh, using the same system independent protocol
modules, but with a user interface that is much more closely related to
the expected Macintosh environment.
Installation documentation for the Mac is included with the Mac version
of the software, available from <insert contact info here>.
2.6. Atari ST
Installation for the Atari version of NET is not yet available. Your
best bet is to stare at the sources, in config.h and files.h, as well as
st.c and st.h. We hope to include documentation in the next revision of
this manual.
2.7. NEC PC-9801
Installation on the NEC PC-98 family is the same as for the IBM PC and
clones, except that you need to have the version of NET.EXE that
includes handling for the serial port(s) in the NEC machine.
2.8. Hewlett-Packard Portable Plus
Installation on the Portable Plus is the same as for the IBM PC and
clones, except that you need to have the version of NET.EXE that is
designed for the Portable Plus.
- 39 -
3. Taking NET for a Test Drive
For the quick introduction to NET provided in this section, we assume
that you are using an IBM PC or clone with the Plug'n'Play disk. We also
assume that you've already configured the disk per in the installation
instructions. Finally, we assume a TNC has been set up as interface
'ax0'.
3.1. Trying out the AX.25 Support
Start by typing 'NET' to get the program up and running. You should be
presented with a banner including revision information and a copyright
statement, followed by a prompt of 'net>'. If you don't get this, some-
thing is horribly wrong. Find a friend and ask for help.
Once you have the program going at all, the first thing you'll probably
want to do is to figure out if the TNC is hooked up correctly, and
whether you're getting out at all. To get connected, you do basically
the same thing you'd do with a raw TNC. Type 'connect ax0 <callsign>',
where <callsign> is someone's callsign who is known to be on the air.
You can also specify a digipeater string. For example, you could type
one of:
connect ax0 n3eua (connect using the ax0 TNC to N3EUA)
connext ax0 n3eua n1fed n0ccz (conn to N3EUA via N1FED and N0CCZ)
If all is well, you should get "Conn Pending" and then "Connected" mes-
sages. At this point, you're connected just like using a plain old TNC.
Kind of boring, huh? It'll get more exciting soon!
When you're ready to disconnect, use the <F10> key to escape from the
session back to the 'net>' prompt, and then type 'disconnect'. You will
discover that all commands can be abbreviated, and you can type a
If things don't work, watch the lights on the TNC to see if you're
transmitting at all, then go read up on the "trace" command so you can
see what the program thinks it's doing. Even easier, if there's someone
else using TCP in your area, ask for help!
3.2. The Telnet Command
If there's someone else on the air in your area already using TCP/IP,
then the next most easy thing to do is to try a keyboard connection
using the Telnet protocol. The end result will be the same as doing an
AX.25 connect in most cases, but you'll be taking advantage of a couple
of neat attributes of having more protocol horsepower to help you out.
First, you need to either know the numeric IP address of your friend's
system, or you need to have updated HOSTS.NET to include the system name
and the numeric address. Then all you have to do is type:
telnet n3eua (talk to N3EUA, address in HOSTS.NET) tel-
net [44.32.0.4] (use the numeric address directly)
- 40 -
Now you can type back and forth just as if you were connected with a
normal TNC. When you're done, use the <F10> key to escape back to com-
mand mode, and then type 'close' to close the connection gracefully, or
'reset' if you're really in a hurry.
3.3. The FTP Command
So far, all we've done is to use more software and work harder to do the
same things we can do with a plain old TNC. The FTP command isn't like
that! If you want to get a file from your friends' machine, you can
type the command:
ftp n3eua
to start a file transfer session to the N3EUA machine. When the connec-
tion is opened, you'll get a banner from the remote machine, followed by
a prompt for your user name. If you've negotiated with your friend to
have a special username and password set up for you in his FTPUSERS
file, use that. If not, many machines allow arbitrary users to get lim-
ited access to the files available with a special username 'anonymous'.
If you want to use the 'anonymous' login, when you're prompted for a
password enter your callsign or something else recognizable, as many
folks keep a log of FTP's so they know what files people care about, and
being able to associate your activities with you sometimes helps.
3.4. The Mail System
The mail system is a subject unto itself. It is also one of the truly
nifty things about running TCP/IP. Look elsewhere in the documentation
for a complete rundown on how to install and operate the BM mailer, and
the portions of NET related to it.
3.5. Tracing and Status Commands
The tracing and status commands provide a great deal of information
about what is going on in the system. All we'll attempt to do here is
raise your interest level.
If you want to find out what sessions are active to and from your
machine, you can type 'sessions' and you'll get a list. If you want to
get information about all of the TCP connections open to and from your
machine, including mail transfers and other things that don't directly
interact with your keyboard and screen, you can type "tcp status" and
you'll get a list of connections.
If you're not sure what's happening on an interface, or you'd like to
"read the mail" (watch what other folks are doing ont he channel), then
use the "trace" command. The form is descibed in the command reference
elsewhere in this document. For example:
trace ax0 111 (activity on ax0, including ASCII dump) trace
ax0 211 (activity on ax0, including hex dump) trace ax0 11
(activity on ax0, printing only the headers)
Note that you also have control over whether tracing can bother you in a
- 41 -
session, see the trace command summary for more details.
- 42 -
4. The Mail System
As is typical with networking software, handling electronic mail is
often as big a job as coping with all other applications combined. In
order to make full use of the mail system in the KA9Q package, you will
need to spend a little time getting things configured for your system.
4.1. Installing and Using BM
The BM.EXE mail user interface program was created by Bdale Garbee,
N3EUA, and despite popular belief, 'BM' really stands for "Bdale's
Mailer". Gerard van der Grinten PA0GRI extended the mailer with a
number of new features that resulted in version 2. More recently, Dave
Trulli NN2Z has extended the mailer creating revision 3. All comments
or suggestions about BM should be directed to Dave.
BM provides a full set of mail services to the user which allow sending
and receiving electronic mail, as well as a variety of local mail mani-
pulation commands.
4.1.1. Installation
To install BM requires the modification of the supplied configuration
files and the creation of the proper directory structure. The fol-
lowing sections describe the file and directory structure used by BM
and SMTP.
4.1.1.1. Directory Structure
/spool/mqueue This directory holds the outbound mail
jobs for SMTP. Each job consists of 2
files a xxxx.txt and xxxx.wrk file where
xxxx is a unique numerical prefix. The
format of the files are described in a
later section.
/spool/rqueue This directory is used by SMTP for jobs
that have been received and will be
processed by a user defined mail routing
program. This directory is not used
directly by BM.
/spool/mail This directory holds the individual
mailboxes for each user name on your
system. The extension .txt is add to the
user name to form the mailbox name. Mail
received by the SMTP server is appended to
the mailbox file.
4.1.1.2. Configuration File
The /bm.rc file provides BM with the configuration needed for the
operation of the mailer.
- 43 -
The format for the /bm.rc file is:
variable <space> value <newline>
The following variables are valid in the bm.rc file:
4.1.1.2.1. smtp <path>
Defines the path to the directory containing the mailbox files. The
default directory is /spool/mail on the current drive.
4.1.1.2.2. host <your hostname>
Is used to set the local hostname for use in the RFC822 mail headers.
This is a required field. This should match the hostname definition in
autoexec.net.
4.1.1.2.3. user <username>
Defines the user name of the person who is sending mail. This is also
used as the default mailbox for reading mail. On the AMPRNET this is
usually set to your call. There is a DOS limit of 8 characters for the
user name.
4.1.1.2.4. edit <path of your editor>
Defines the name of your favorite editor which can be used to construct
and edit the text of outgoing messages. The use of edit is optional.
4.1.1.2.5. fullname <your full name>
Is used to provide your full name to the mailer for use in the comment
portion of "From:" header line. The use of fullname is optional.
4.1.1.2.6. reply <return address>
Defines the address where you wish to receive replies to messages
sent. This option is useful if you are operating your pc on a local
area network and would like your mail replies sent to a more "well
known host". The address specified by reply is used to generate a
"Reply-To:" header in outbound mail. The "Reply-To:" header overrides
the "From:" header which is the address normally used to reply to
mail. This field is optional.
4.1.1.2.7. maxlet <number of messages>
defines the maximum number of messages that can be processed by
BM in one mailbox file. The default value of maxlet is 100.
4.1.1.2.8. mbox <filename>
Specifies the default file to be used for the "save" command.
This file is in the same format as a mailbox and may later be viewed
- 44 -
using the -f option of BM. If this option is not used then the
default is set to mbox.
4.1.1.2.9. record <filename>
If defined a copy of each message sent will be saved in <filename>.
4.1.1.2.10. folder <directory name>
If defined folder contains the path used by the save command.
4.1.1.2.11. screen [bios|direct]
In the Turboc compiled version of BM, screen sets the display out-
put mode to use either direct writes to screen memory or the ROM BIOS.
The default is direct which provides the fastest output mode.
If you are using a windowing system such as Desqview you should set the
mode to bios.
4.1.1.2.12. Example BM.RC File
host nn2z.ampr user dave fullname Dave Trulli # send my replies to
the Sun reply nn2z@ka9q.bellcore.com screen direct edit /bin/vi
mbox c:/folder/mbox record c:/folder/outmail folder c:/folder max-
let 200
4.1.1.3. The ....lias File
The alias file provides an easy way to maintain mailing lists. An
alias can be any string of characters not containing the "@" symbol.
The format for the alias file is:
alias recip1 recip2 recip3
<tab> recip4
Note that a long list of aliases can be continued on an additional
line by placing a tab or space on the continuation line.
Some examples aliases are:
dave nn2z@nn2z.ampr
phil karn@ka9q.bellcore.com
# mail to local nnj users
nnj wb2cop@wb2cop.ampr karn@ka9q.bellcore.com
wb0mpq@home.wb0mpq.ampr w2kb@w2kb.ampr
In the above example, when specifying nnj as the recipient,
BM will expand the alias into the list of recipients from the alias
file. At this time an alias may not contain any other aliases.
- 45 -
4.1.1.4. /spool/mqueue/sequence.seq The sequence file maintains a mes-
sage counter which is used by BM and SMTP to generate message ids and
unique filenames. This file is created if not already present by BM.
4.1.2. Environment
The timezone used in mail headers is obtained from the DOS environment
variable TZ. An example TZ setting is:
set TZ=EDT4
It is set in your AUTOEXEC.BAT file. The first 3 characters
are the timezone and the fourth character is the number of hours from
GMT time. If TZ is not set, GMT is assumed.
4.2. Commands
All BM commands are single letters followed by optional arguments.
The command list has been designed to make those familiar with Berke-
ley mailers comfortable with BM.
4.2.1. Main Menu Commands
4.2.1.1. m [userlist]
The mail command is used to send a message to one or more recipients.
All local recipient names ( those which don't contain an '@' ) are
checked for possible aliases. If no arguments are supplied you
will be prompted for a recipient list. While entering a message
into the text buffer several commands are available such as: invoking
an editor, and reading in text from other messages or files. See the
section below for a description of these commands. To end a message
enter a line containing a single period.
It is important to remember that the input line buffer has a 128 char-
acter limit. You should format your text by entering a carriage
return at the end of each line. Typing excessively long lines may
cause data loss due to truncation when passing the message through
other hosts. Keeping lines less than 80 characters is always a
good idea.
4.2.1.2. d [msglist]
Mark messages for deletion. Messages marked for deletion are removed
when exiting BM via the 'q' command or when changing to an alternate
mailbox with the 'n' command.
4.2.1.3. h
Display message headers. The message headers contain the message
number, the status indicating whether it has been read or deleted, the
sender, size, date, and subject.
- 46 -
4.2.1.4. u [msglist]
Undelete a message that is marked for deletion. The status of a mes-
sage can be determined by looking at the status field of the message
using the 'h' command.
4.2.1.5. n [mailbox]
Display or change mailbox. The 'n' command with no arguments will
display a list of mailboxes containing mail. If an argument is sup-
plied, then the current mailbox is closed and a new mailbox is opened.
4.2.1.6. ! cmd
Run a DOS command from inside BM. An error message will result if
there is not enough memory available to load the command.
4.2.1.7. ?
Print a help menu for BM commands.
4.2.1.8. s [msglist] [file]
The 's' command is used to save messages in a file. If no filename
is given the default from the mbox variable in /bm.rc is used. If no
message number is supplied then the current message is saved. The
message is stored in the same format as a mailbox file with all mail
headers left intact.
4.2.1.9. p [msglist]
The 'p' command is used to send messages to the printer. This com-
mand uses the DOS device PRN for output. This command is equivalent
to:
s [ msglist ] PRN
4.2.1.10. w [msglist] file
The 'w' command is used to save messages in a file. Only the message
body is saved. All mail headers are removed. If no message number is
supplied then the current message is saved.
4.2.1.11. f [msg]
The 'f' command is used to forward a mail message to another recipient.
If no message number is supplied the current message is used. The user
is prompted for the recipients and a subject. The RFC822 header is
added to the message text while retaining the complete original message
in the body. Also see the ~m command.
4.2.1.12. b [msg]
Bounce a message. Bounce is similar to forwarding but instead of
your user information, the original sender information is
- 47 -
maintained. If no message number is supplied the current message
is used.
4.2.1.13. r [msg]
Reply to a message. Reply reads the header information in order to
construct a reply to the sender. The destination information is taken
from the "From:" or the "Reply-To:" header, if included. If no
message number is supplied the current message is used.
4.2.1.14. msg#
Entering a message number from the header listing will cause the
message text to be displayed.
4.2.1.15. l
List outbound messages. The job number, the sender, and the destina-
tion for each message is displayed. A status of "L" will appear if the
SMTP sender has the file locked.
4.2.1.16. k [msglist]
Remove an outbound message from the mqueue. A message can be removed
from the send queue by specifying the job number obtained by the l
command. If the message is locked you will be warned that you may
be removing a file that is currently being sent by SMTP. You will
asked if this job should still be killed.
4.2.1.17. $
Update the mailbox. This command updates the mailbox, deleting
messages marked for deletion and reading in any new mail that may have
arrived since entering BM.
4.2.1.18. x
Exit to DOS without changing the data in the mailbox.
4.2.1.19. q
Quit to DOS updating the mailbox.
4.2.2. Text Input Commands
The following commands are available while entering message text
into the message buffer.
~r <filename> read <filename> into the message buffer.
~m <msg #> read <msg #> into the message buffer.
~p display the text in the message buffer.
- 48 -
~e invoke the editor defined in /bm.rc with a
temporary file containing the text in the
message buffer.
~q Abort the current message. No data is sent.
~~ Insert a single tilda character into the
message.
~? Display help menu of tilda escape commands.
4.2.3. Command Line Options BM may be invoked as follows:
To send mail:
bm [ -s subject ] recip1 .. .. recipN
To read mail:
bm [ -u mailbox | -f file ]
-s subject This option sets the subject to the text on
the command line.
-u mailbox Specify which mailbox to read. This
overides the default from the bm.rc.
-f file Read message from "file" instead of a
mailbox.
4.3. Technical Information
4.3.1. Outbound Mail Queue File Formats
Outgoing mail messages consist of two files each in the /spool/mqueue
direc- tory. The names of the two files will be of the form
<integer>.WRK and <integer>.TXT, where integer is the sequence number of
the message relative to this machine. The file sequence.seq in the
mqueue directory contains the current sequence number for reference by
the mail user interface. The .TXT file contains the data portion of
the SMTP transaction, in full RFC822 format. The .WRK file consists of
3 or more lines, as follows:
the hostname of the destination system
the full sender address, in user@host format.
some number of full destination addresses, in user@host format.
4.3.2. Standards Documents
The SMTP specification is RFC821. The Format for text messages (includ-
ing the headers) is in RFC822. RFC819 discusses hostname naming conven-
tions, particularly domain naming.
- 49 -
4.4. Bug Reports
Please send any comments, suggestions or bug reports about BM to:
Dave Trulli Usenet: nn2z@ka9q.bellcore.com packet: nn2z@nn2z
AMPRNET: nn2z@nn2z.ampr [44.64.0.10]
- 50 -
5. NET/ROM Support
5.1. Introduction The NET/ROM support for the KA9Q package serves three
purposes:
1) Existing NET/ROM networks may be used to send IP traffic.
2) NET may be used as a NET/ROM packet switch.
3) NET may be used to communicate with NET/ROM nodes, and its
mailbox facility can accept connects over the NET/ROM net-
work.
5.2. Setting up the NET/ROM Interface
No physical interface is completely dedicated to net/rom, which is as
it should be. You attach all your AX.25 interfaces, of whatever sort.
Then you attach the net/rom pseudo-interface ("attach netrom"). Then
you identify to the net/rom software those interfaces you want to allow
it to use, with the "netrom interface" command. The format of this com-
mand is:
netrom interface ax0 #ipnode 192
The first argument is the name of the previously attached interface you
want to use. The second argument is the alias of your node, to be used
in your routing broadcasts. The alias is never used for anything else
(as you will see!). The last number is the net/rom quality figure.
This is used in computing the route qualities; it represents the contri-
bution of this interface to the overall computation. For a 1200 baud
half-duplex connection, 192 is the right number.
You need a netrom interface command for every interface you're going
to use with net/rom.
5.3. Tracing on the NET/ROM Interface
If you want to trace your NET/ROM datagrams, don't try turning on
trace mode for the "netrom" interface. Nothing will break, but nothing
will happen. You should trace the individual AX.25 interfaces instead.
5.4. Routing Broadcasts
Once you have set up your interfaces, you need to set some timers.
There are two: the nodes broadcast interval timer, and the obsolescence
timer. These are set in seconds, like the smtp timer. You should usu-
ally set them to an hour. You can set them to something different, if
you want. If your local net/rom nodes broadcast every hour, but you
want to do so every ten minutes, you can say:
netrom nodetimer 600 netrom obsotimer 3600
Every time the obsotimer kicks, the obsolescence counts for all non-
permanent entries are decremented by one. When the count for an entry
- 51 -
falls below five, it is no longer broadcast. When it falls to 0, it is
removed. The count is initialized at 6. These will eventually be sett-
able parameters; you can adjust them now by changing the initializers
for the variables in the source file.
When you first come on the air, you can send out nodes broadcasts to
tell the local nodes that you are available. Use the command:
netrom bcnodes ax0
where ax0 is the interface on which you want to send the broadcast. Do
this for every interface on which you want to do this.
By default, the NET/ROM code does not broadcast the contents of your
routing table. This is as it should be, since usually we just want to
be the endpoints of communications rather than relaying NET/ROM traffic.
If you want to be a switch station, include the command:
netrom verbose yes
in your autoexec.
Sometimes you can hear broadcasts from nodes that can't hear you. If
your routing table gets filled with these unusable routes, your node
will grind to a halt. The solution to this is node broadcast filtering,
via the netrom nodefilter command. There is a filter list, which con-
tains a list of callsigns and interfaces. Then there is a filter mode,
which indicates what to do with the list.
If the filter mode is "none", no filtering is done. If it is
"accept", then only broadcasts from the indicated stations on the indi-
cated interfaces are accepted. If it is "reject", then all broadcasts
except those from the listed stations on the listed interfaces are
accepted.
Because the net/rom code cannot at this time recognize unusable
routes and try alternates, I strongly recommend use of the filter com-
mand to restrict broadcast acceptance to those nodes which you know you
can reach.
5.5. The NET/ROM Routing Table
The next net/rom commands are those used for maintaining the routing
table. They fall under the "netrom route" subcommand. "netrom add"
adds a permanent entry to the routing table. Its format is:
netrom route add #foo w9foo ax0 192 w9rly
This command adds an entry for w9foo, whose alias is #foo, route quality
192, via w9rly on interface ax0. Let's talk about what this means.
w9foo is the *destination* node, the one to whom you want the packets
routed by the net/rom network. w9rly is your *neighbor*, the net/rom
node to which you pass the packet to be forwarded. Since w9rly may
appear on more than one interface (the callsign may be used by more than
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one net/rom node on different bands), we specify that we are to use ax0
to send the packet.
With net/rom, like IP, we don't know exactly what route a packet will
take to its destination. We only know the name of a neighbor which has
indicated a willingness to forward that packet (of course, the neighbor
may be the destination itself, but that's unlikely in our application).
Net/rom sends the packet to the neighbor, with a network header specify-
ing our callsign and that of the ultimate destination (in this case
w9foo).
We can use the netrom route add command to establish a digipeater
path to the neighbor. For example:
netrom route add #foo w9foo ax0 192 w9rly wd9igi
This will cause us to use wd9igi as a digipeater in establishing our
connection to the net/rom node w9rly.
To drop the route to w9foo, you would type
netrom route drop w9foo w9rly ax0
To see the contents of your routing table, you may type
netrom route
and to see the routing entries for an individual station you can type
netrom route info <callsign>
You may not use an alias as an argument to the netrom route info com-
mand.
I can not stress enough that "route add" and "netrom route add" are
two different commands, with different purposes. In general, you only
need a "netrom route add" if you need to add a route to a net/rom node
via a digipeater path. If you find yourself using this command, ask
yourself, "Why am I doing this?" Many people do not understand that
net/rom does automatic routing (well, sort of :-)).
5.6. The Importance of the Routing Table
The NET/ROM routing table is analogous to the IP routing table: if
there is nothing in it, your NET/ROM traffic will not go out. You must
either manually enter a list of routes (perhaps via your autoexec.net)
or wait to receive routing broadcasts from your neighbors before your
NET/ROM traffic will leave your station.
If you go to send packets via NET/ROM and nothing happens, even if
you have trace mode on, make sure that the destination node is in your
NET/ROM routing table. If sending IP traffic, double check the ARP
table for an appropriate NET/ROM ARP entry for the destination node (see
below for more information on the use of the ARP table). The ARP table
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is not used for NET/ROM transport routing.
5.7. Interfacing with NET/ROMs Using Your Serial Port
What if you have a net/rom node or nodes, and you'd like to attach
them to your computer via their serial interfaces, and use net as a
packet switch? It's very easy: you have to attach those interfaces,
using the "attach asy" command, but specifying type "nrs" instead of
"slip" or "kiss". "nrs" is the net/rom serial framing protocol, which
is like KISS, but uses different framing characters and has an 8-bit
checksum.
When you attach an nrs interface, it can be used for passing IP
datagrams or AX.25 frames over serial lines or modems. To use it for
net/rom, you have to identify it to the netrom code just like any other
interface, with the "netrom interface" command.
5.8. The Time to Live Initializer
The "netrom ttl" command allows setting of the time-to-live initial-
izer for NET/ROM datagrams. I recommend a value of 16 for most net-
works. Use more if you expect to go more than 16 hops. The default is
64.
The purpose of the ttl initializer is to prevent a packet from get-
ting caught forever in routing loops. Every router who handles the
packet decrements the ttl field of the network datagram before sending
it on, and when it reaches 0 it is discarded.
5.9. Using NET/ROM Support for IP
Now you know all the commands, but how do we actually use net/rom for
IP communications? This takes two steps:
Step one: update the routing table. In all likelihood, you will use
net/rom to gateway two IP subnets. So, you'll probably want to identify
a station on each end as a gateway. Let's say we're on the Milwaukee
subnet, and we want to talk to someone in Madison. If we're not the
gateway, we just have a routing table entry like this:
route add [44.92.0.0]/24 ax0 wg9ate-pc.ampr
This specifies that wg9ate should get all packets for the 44.92.0.x sub-
net via interface ax0.
Wg9ate has this routing table entry:
route add [44.92.0.0]/24 netrom w9mad-pc.ampr
(presuming that w9mad is the Madison gateway). Now, when the IP layer
at wg9ate gets datagrams for Madison, it knows that they have to go via
net/rom to w9mad. Notice that we don't specify a "real" interface, like
ax1 or nr0, in the route entry. The net/rom network layer will pick the
right interface based on its net/rom routing tables.
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We're not done yet, though. w9mad-pc.ampr is not an ax.25 callsign.
The net/rom send routine called by the IP layer needs to map from the IP
address to an ax.25 address. It does this via a manually added arp
entry:
arp add w9mad-pc.ampr netrom w9mad
[We kind of fudged by using the arp table for this purpose, since there
is no way to do automatic address resolution for net/rom, and arp mes-
sages are never sent or received for net/rom nodes. However, the arp
table does contain precisely what we have here: mappings from IP
addresses to callsigns, and it saved a lot of code to do it this way.]
Notice also that no digipeaters are ever specified in the arp entry for
a net/rom node. Also, the callsign to which we are mapping is the final
destination of the packet, not the non-destination neighbor. That
neighbor will be picked based on the net/rom routing tables.
So, as a summary, let's look at what happens to a packet that reaches
the IP layer on wg9ate, destined for Madison. The IP routing code looks
the destination IP address up in the table, and discovers that it should
go via net/rom to w9mad-pc.ampr. So, it passes the packet to the
net/rom send routine. That routine uses the arp table to translate
w9mad-pc's IP address to the callsign "w9mad". Then it passes the
packet to the net/rom routing code. That code checks to see if the des-
tination callsign (w9mad) is the same as that of any of its assigned
net/rom interfaces. Since it isn't, it puts a network layer header
(a.k.a. net/rom level 3 header) on it, and looks for w9mad in its rout-
ing tables. Presumably, it finds an appropriate neighbor for the
packet, and sends in out via ax.25. The net/rom network does the job of
actually getting the packet to its destination.
At w9mad, the packet's protocol ID causes it to be sent to the same
net/rom routing code that handled the outgoing packet from wg9ate (run-
ning on a different computer, of course). Now the destination callsign
matches, so the net/rom network layer header is stripped off, and packet
is passed up to the IP layer. (Net/rom network headers don't have a
protocol ID byte, so we just hope for the best. If a net/rom node
addresses a net/rom transport layer packet to us, it is likely to be
dropped by IP for any of a number of reasons.)
5.10. The NET/ROM Transport Layer
NET/ROM transport is the protocol used by NET/ROM node to communicate
end-to-end. When a user attaches to a NET/ROM via AX.25, and asks for a
connect to a node in the NODES list, his local NET/ROM tries to open a
transport connection to the destination node over the NET/ROM network.
NET/ROM transport packets are carried in NET/ROM network datagrams, just
like IP datagrams.
You shouldn't use NET/ROM transport when connecting to other TCP/IP
stations. TCP is a much better protocol than NET/ROM transport, and
makes better use of available bandwidth. Also, BM and SMTP are more
convenient to use than a TCP/IP station's mailbox facility. However,
- 55 -
for communicating with AX.25 users via the NET/ROM network, the tran-
sport facilities in NET will work better (and more easily) than the
traditional method of connecting to your local node via AX.25.
5.11. Connecting via NET/ROM Transport
To connect to the node whose alias is FOO and whose callsign is
W9FOO, you can issue either of the following two commands:
netrom connect foo
netrom connect w9foo
If foo:w9foo is in your NET/ROM routing table, your station will
transmit a connect request to the appropriate neighbor used to reach
w9foo.
NET/ROM transport sessions are very much like those for AX.25. You
can use the disconnect, reset, kick, upload, and record commands, and
the session command to switch sessions.
5.12. Displaying the Status of NET/ROM Connections
The command
netrom status
is used to display the status of all NET/ROM connections, which will
include those used in keyboard sessions as well as ones attached to the
mailbox. For more detailed information on a session, you can use the
address of the NET/ROM control block:
netrom status <&nrcb>
where <&nrcb> is the hex address given in the short form of the command
or in the "session" display.
5.13. NET/ROM Transport Parameters
The NET/ROM transport parameters may be set with the various NET/ROM
subcommands. Their meanings are listed below:
acktime: This is the ack delay timer, similary to ax25
t2. The default is 3000 ms.
choketime: The time to wait before breaking a send choke
condition. Choke is the term for
NET/ROM flow control.
irtt: The initial round trip time guess, used for
timer setting.
qlimit: The maximum length of the receive queue for chat
sessions. This is similar to ax25
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window.
retries: Maximum retries on connect, disconnect, and data
frames.
window: Maximum sliding window size, negotiated down at
connect time.
5.14. The Mailbox
The AX.25 mailbox also accepts NET/ROM connections. The "mbox on"
and "mbox off" commands control whether the mailbox is turned on for
NET/ROM as well as AX.25, and the "mbox" command displays current mail-
box connects of both types.
Many people have observed that the AX.25 mailbox requires the user to
enter a carriage return to bring up the banner and prompt. This is
because of certain defects of that protocol when it is used as the link
layer for several different higher level protocols, and is unavoidable.
(So stop asking, OK? :-)) The NET/ROM mailbox does not require the car-
riage return, and will be activated as soon as the incoming connection
is completed.
5.15. Where to go for More Information
The paper "Transmission of IP Datagrams over NET/ROM Networks"
appeared in the Seventh ARRL Networking Conference papers, available
from the ARRL. In it, I describe the more technical details of how the
NET/ROM network support works.
If you want to learn about NET/ROM, talk your local NET/ROM or TheNET
operator out of his or her manual. If you want to learn more, read the
source code. That's about it for sources, since the NET/ROM protocols
originated in a commercial product.
5.16. About the Code
There has been a great deal of controversy about TheNET, a no-charge
NET/ROM clone for TNCs. This is not the place to discuss the truth of
the charges leveled by Software 2000 against its authors, but that
situation requires me to make the following statement:
The NET/ROM transport support in NET.EXE was not taken in any way,
shape or form from NET/ROM (whose source I have never seen) or from
TheNET. The protocol code is based on protocol 6 from Tanenbaum's
excellent book, Computer Networks, as a moderately careful reading of
both should show. The source code is freely distributed, so the curious
reader should have the opportunity to check this assertion if he or she
so desires.
The smoothed round trip time calculation, which is not done in "real"
NET/ROMs (and should be, by the way -- they'd work a whole lot better)
is adapted from that used by KA9Q in the TCP protocol in NET. The dicey
- 57 -
business of adapting it to a sliding windows protocol with selective
retransmission was done by me, all alone, after my cries for help on the
tcp-group mailing list went unanswered :-).
I have taken the precaution of copyrighting the NET/ROM code in NET.
It may be freely distributed for non-commercial purposes, in whole or in
part, and may be used in other software packages such as BBS systems if
so desired, so long as the copyright notice is not removed from the
source files, and the program in which it is used displays "NET/ROM code
copyright 1989 by Dan Frank, W9NK" when it starts up.
Any person who wishes to distribute the code, or anything based on
the code, for commercial purposes will find me very reasonable, but
rather insistent about being compensated for the hours I've spent work-
ing on it.
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6. Advanced Topics
6.1. The Finger Server
< there will be finger docs here someday >
6.2. The GRAPES Multi-Port Digipeating Code
The multiport digipeating code from GRAPES will allow you to route
frames in and out of LANs semi-automagically based on a table lookup
maintained by the switch.
To enable multi-port digipeating, there are two tables that you must
build and place in the root directory. They are named DIGILIST and
EXLIST. DIGILIST contains the digis that are directly reachable from
your switch. The file is a simple ASCII text file containing the
callsign of the digi and the interface name of the port needed to
reach it. The port name is the same name you used in the attach state-
ment for that port. Additionally there is a special callsign "lan" that
tells mulport which port feeds your LAN or default port.
The file would look something like this:
kd4nc-1 ax1 # kd4nc-1 is a neighbor switch on the high speed link
# attached to ax1 wb4gqx-1 ax3 # wb4gqx-1 is a
neighbor digi on 145.01 (ax3) k4hal-1 ax2 # k4hal-1 is a neighbor
digi on 440 (ax2) lan ax0 # lan is a special name for the low
speed lan
# attached to the switch and is the default port
# used when mycall is the last call in the digi
# string.
The file EXLIST holds DESTINATION callsigns that do not obey the rules.
For example, a user station on the high speed link. It is formatted
just like DIGILIST. To understand why this file may be necessary we
review the rules mulport obeys. First, mulport examines the digi string
of incoming frames. If it finds it's call in the string and it is not
already marked as repeated, it looks at the next call in the digi
string. If a match is found between the call following MYCALL in
the digi string and a call in DIGILIST, then the frame is repeated out
the port associated with that call in DIGILIST. If no match is found
then the frame is repeated out the port it came in on. If MYCALL is the
LAST call in the digi string then it repeats the frame out the port
associated with "lan" in the DIGILIST. So you see that if MYCALL is
the last or the only call in the digi string the frame will be
repeated out the lan port. This can cause a problem if the station you
wish to connect is only one digi hop away and is not on the lan fre-
quency. The EXLIST handles this case. Mulport will look at the DES-
TINATION call if MYCALL is the last or only call in the digi string. If
a match is found with a call in EXLIST then the port associated with
that DESTINATION call is used to repeat the frame. EXLIST is only for
stations who would normally be expected to be on the lan side but are
operating off some other port instead. An example might be a PBBS
operating on the trunk to serve more than one lan.
- 59 -
6.3. Multiple Serial Ports on One Interrupt
Thanks to effort from Dan Frank, W9NK, this version of net supports the
idea of multiple serial ports all sharing a common hardware interrupt
line. The original motivation for this was to support the IBM PS/2 fam-
ily, but it turns out to be very helpful with a variety of PC/AT inter-
face cards as well.
There are no new commands, and existing autoexecs don't need to be
changed. All you have to do to share interrupts is simply use the same
interrupt in more than one attach line. This applies *only* to asy dev-
ices. An interrupt may not be shared between, e.g., an ethernet card and
a serial port.
The code has been tested on an IBM PS/2 Model 70 with the dual async
adaptor. Any card that logical-ORs the interrupt lines from the various
UARTS should work.
Interrupt sharing at the bus level does not work on the AT bus, but does
work on the Micro Channel. The PS/2 series uses interrupt 4 for the
motherboard async port, then interrupt 3 for all bus-attached serial
ports.
The code is believed to work with both level-sensitive and edge-
triggered interrupts, but hasn't been fully tested.
As an example, the Quadram Quadport AT with the add-on daughtercard can
handle up to five serial ports sharing the same interrupt, and up to two
cards may be supported in a PC, making a total of more serial ports than
a poor little PC should be asked to handle...
- 60 -
7. NET Command Reference
7.1. Startup
When NET.EXE is executed without arguments, it attempts to open the
file "AUTOEXEC.NET" in the root directory of the current drive. If it
exists, it is read and executed as though its contents were typed on the
console as commands. This feature is useful for setting the local IP
address and host name, initializing the IP routing table, and starting
the various Internet services. If NET.EXE is invoked with an
argument, it is taken to be the name of an alternate startup file; it is
read instead of AUTOEXEC.NET.
7.2. Console Mode
The console may be in one of two modes: command mode and converse
mode. In command mode, the prompt "net>" is displayed and any of the
commands described in the next section may be entered. In converse mode,
keyboard input is processed according to the "current session", which
may be either a Telnet, FTP, or AX.25 connection. In a telnet or AX.25
session, keyboard input is sent to the remote system and any output
from the remote system is displayed on the console. In an FTP session,
keyboard input is first examined to see if it is a known local com-
mand; if so it is executed locally. If not, it is "passed through" to
the remote FTP server. (See the section titled "FTP Subcommands").
The keyboard also has "cooked" and "raw" states. In cooked state, input
is line-at-a-time; the user may use the line editing characters ^U, ^R
and backspace to erase the line, redisplay the line and erase the
last character, respectively. Hitting either return or line feed passes
the complete line up to the application. In raw mode, each character is
immediately passed to the application as it is typed. The keyboard is
always in cooked state in command mode. It is also cooked in converse
mode on an AX25 or FTP session. In a Telnet session it depends on
whether the remote end has issued (and the local end has accepted) the
Telnet "WILL ECHO" option. (See the "echo" command).
On the IBM-PC, the user may escape back to command mode by hitting
the F10 key. On the HP Portable and Portable Plus, which have only 8
function keys, F8 is used instead. On other systems, the user must
enter the "escape" character, which is by default control-] (hex 1d,
ASCII GS). (Note that this is distinct from the ASCII character of
the same name). The escape character can be changed (see the "escape"
command).
7.3. Commands
This section describes each of the commands recognized while in command
mode. Note that certain FTP subcommands, e.g., put, get, dir, etc,
are recognized only in converse mode with the appropriate FTP session;
they are not recognized while in command mode. The notation "<hos-
tid>" denotes a host or gateway, which may be specified in one of two
ways: as a symbolic name listed in the file "/hosts.net", or as a
numeric IP address in dotted decimal notation enclosed by brackets,
- 61 -
e.g., [44.0.0.1]. When domain server support is added, ARPA-style
domain names (e.g., ka9q.ampr) will also be accepted if a domain
server is available on the network to resolve them into IP addresses.
7.3.1. <cr>
Entering a carriage return (empty line) while in command mode puts you
in converse mode with the current session. If there is no current
session, net remains in command mode.
7.3.2. !
An alias for the "shell" command.
7.3.3. #
Commands starting with the hash mark (#) are ignored. This is mainly
useful for comments in the AUTOEXEC.NET file.
7.3.4. arp
With no arguments, displays the Address Resolution Protocol table that
maps IP addresses to their subnet (link) addresses on subnetworks
capable of broadcasting. For each IP address entry the subnet type
(e.g., Ethernet, AX.25), subnet address and time to expiration is
shown. If the link address is currently unknown, the number of IP
datagrams awaiting resolution is also shown.
7.3.4.1. arp add <hostid> ether|ax25|netrom <ether addr|callsign>
The add subcommand allows manual addition of address resolution entries
into the table. This is useful for "hard-wiring" digipeater paths, and
other paths that are not directly resolvable.
7.3.4.2. arp drop <hostid> ether|ax25|netrom
The drop subcommand allows removal of entries from the table.
7.3.4.3. arp publish <hostid> ether|ax25|netrom <ether addr|callsign>
The publish subcommand allows you to respond to arp queries for some
other host. This is commonly referred to as "proxy arp", and is con-
sidered a fairly dangerous tool. The basic idea is that if you have two
machines, one of which is on the air with a TNC, and the second one of
which is connected to the first with a slip link, you might want the
first machine to publish it's own AX.25 address as the right answer for
arp queries addressing the second machine. This way, the rest of the
world doesn't know the second machine isn't really on the air. Use arp
publish with caution.
7.3.5. attach
attach <hwtype> <I/O addr> <vector> <mode> <label> <bufsize> <mtu>
[<speed>]"
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Configure and attach a hardware interface to the system.
<hw type> represents the kind of I/O device that is being attached.
The following types are some that are supported:
packet FTP, Inc., compatible Packet Driver Interface 3c500 3Com 3C500
or 3C501 Ethernet interface asy Standard PC asynchronous interface
using the National 8250 hapn Hamilton Amateur Packet Network adapter
board (Intel 8273) eagle Eagle Computer card (Zilog 8530) pc100 PAC-
COMM PC-100 (Zilog 8530)
These last two interfaces are still under development; driver code
included in this package may or may not work.
<I/O address> is the base address of the control registers for the dev-
ice.
<vector> is the interrupt vector number. Both the address and the
vector must be in hexadecimal. (You may put "0x" in front of these two
values if you wish, but note that they will be interpreted in hex even
if you don't use it).
<mode> controls how IP datagrams are to be encapsulated in the
device's link level protocol; i.e., it selects among several link proto-
cols that may be available. The choices here depend on the interface;
at present, the 3c500 interface only supports mode "arpa", which uses
standard ARPA-style encapsula- tion. (In the future, "802" may mean
"use 802.3-style encapsulation"). Two modes for the "asy" device are
currently supported:
slip Encapsulates IP datagrams directly in SLIP frames without a link
header. This is for operation on point-to-point lines and is
compatible with 4.2BSD UNIX SLIP).
ax25 Similar to slip, except that an AX.25 header and a KISS TNC
control header are added to the front of the datagram before
SLIP encoding. Either UI (connectionless) or I
(connection-oriented) AX.25 frames can be used; see the
"mode" command for details.
The Address Resolution Protocol (ARP) maps IP to Ethernet addresses on
Ethernet controllers and to AX.25 addresses on "asy" lines operating in
"ax25" mode.
<label> gives the name by which the interface will be known to the
various commands, such as "connect", "route" and "trace".
For asynchronous ports, <bufsize> specifies the size of the ring buffer
in bytes to be statically allocated to the receiver; incoming bursts
larger than this may (but not necessarily) cause data to be lost. For
Ethernet, <bufsize> specifies how many PACKETS may be queued on the
receive queue at one time; if this limit is exceeded, further received
packets will be discarded. This is useful to prevent the system
from running out of memory should another node suddenly develop a case
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of diarrhea.
<mtu> is the Maximum Transmission Unit size, in bytes. Datagrams
larger than this limit will be fragmented at the IP layer into
smaller pieces. For AX.25 UI frames, this limits the size of the infor-
mation field. For AX.25 I frames, however, the ax25 paclen parameter
is also relevant. If the datagram or fragment is still larger than
paclen, it is also fragmented at the AX.25 level (as opposed to
the IP level) before transmission. (See the "ax25 paclen" command
for further information).
<speed> is needed only for an "asy" line; the controller will be
initial- ized to the given speed.
Examples:
# Attach a 3Com Ethernet controller using the standard 3Com address and
# vector (i.e., as it comes out of the box) to use ARPA-standard
# encapsulation. The receive queue is limited to 5 packets, and
# outgoing packets larger than 1500 bytes will be fragmented
attach 3c500 0x300 3 arpa ec0 5 1500
# Attach the PC asynch card normally known as "com1" (the first
# controller) to operate in point-to-point slip mode at 9600 baud,
# calling it "sl0". A 1024 byte receiver ring buffer is allocated.
# Outgoing packets larger than 256 bytes are fragmented.
attach asy 0x3f8 4 slip sl0 1024 256 9600
# Attach the secondary PC asynch card ("com2") to operate in AX.25
# mode with an MTU of 576 bytes at 9600 baud with a KISS TNC,
# calling it "ax0". By default, IP datagrams are sent in UI frames
attach asy 0x2f8 3 ax25 ax0 1024 576 9600
(Note that you cannot use the second asynch controller ("com2") and a
3Com Ethernet card with standard addressing at the same time because
they both use interrupt vector 3).
7.3.5.1. HP Portable Specifics For the unwary, the following are the
correct I/O address values for the HP Portable and Portable Plus... note
that the <vector> is unimportant, but must be included for the line
parsing to work correctly.
HP Portable Plus Serial Port 0x44 HP Portable Plus Modem
Port 0xa4 HP Portable 0xa4
7.3.5.2. SLIP Modem Dialing
An extension to the attach command allows the syntax:
attach <hw type> <I/O address> <vector> <mode> <label> <bufsiz> <mtu>
[<speed>] [[optional '-' for debug] <send> <expect> <send>
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[...]]
for slip connections only. The send/expect sequences allow you to dial a
modem on the slip port, and negotiate a remote login to setup a slip
link.
- - desend carriagedreturn - N s-ndsendwNULL
E - send control-D - send space (not
really needed as the cmdparse routine
allows quoting) \ - send backslash
Note that an expect does not have to follow the last send. Those fami-
liar with UUCP will recognize the expect/send paradigm as being similar
to that used in the L.sys or Systems file.
7.3.6. ax25
7.3.6.1. ax25 digipeat [on|off]
Controls whether AX.25 packets addressed to this station as a digi-
peater will be repeated.
7.3.6.2. ax25 heard [on|off]
Works like the 'mheard' function in many TNC's. The command with no
parameter dumps the list of callsigns heard, with an option you control
whether the list is updated or not.
7.3.6.3. ax25 maxframe [<val]>]
Establishes the maximum number of frames that will be allowed to
remain unacknowledged at one time on new AX.25 connections. This number
cannot be greater than 7.
7.3.6.4. ax25 mycall [<call>]
Display or set the local AX.25 address. The standard format is
used, e.g., KA9Q-0 or WB6RQN-5. This command must be given before any
attach command using AX.25 mode are given.
7.3.6.5. ax25 bbscall [<call>]
Same as mycall, but sets the callsign of the W2XO BBS. This subcommand
is only accessible when you compile net with XOBBS and SID2 defined. The
default is to use a single callsign/ssid for both NET and the PBBS.
7.3.6.6. ax25 paclen [<val>]
Limits the size of I-fields on new AX.25 connections. Note that
if IP datagrams or fragments larger than this are transmitted, they will
be transparently fragmented at the AX.25 level, sent as a series of
I frames, and reassembled back into a complete IP datagram or frag-
ment at the other end of the link. This parameter should be less than
- 65 -
the MTU of the associated interface.
7.3.6.7. ax25 pthresh [<val>]
Sets threshold for transmit without <cr>.
7.3.6.8. ax25 reset <axcb>
Deletes the AX.25 connection control block at the specified address.
7.3.6.9. ax25 retry [<val>]
Limits the number of successive unsuccessful retransmission attempts on
new AX.25 connections. If this limit is exceeded, link re- estab-
lishment is attempted. If this fails "retry" times, then the connec-
tion is abandoned and all queued data is deleted.
7.3.6.10. ax25 status [<axcb>]
Without an argument, displays a one-line summary of each AX.25 control
block. If the address of a particular control block is speci-
fied, the contents of that control block are dumped in more detail.
Note that the send queue units are frames, while the receive queue units
are bytes.
7.3.6.11. ax25 t1|t2|t3 [<val>]
Display or set the AX.25 timers to be used for new connections. T1
is the retransmission timer, T2 is the acknowledgement delay timer and
T3 is the idle "keep alive" timer. Values are in seconds.
7.3.6.12. ax25 window [<val>]
Sets the number of bytes that can be pending on an AX.25 receive
queue beyond which I frames will be answered with RNR (Receiver Not
Ready) responses. This presently applies only to suspended interactive
AX.25 sessions, since incoming IP datagrams are always processed immedi-
ately and not allowed to remain on the receive queue.
7.3.7. close [<session #>]
On an AX.25 session, this command initiates a disconnect. On a FTP or
Telnet session, this command sends a FIN (i.e., initiates a close) on
the session's TCP connection. This is an alternative to asking the
remote server to initiate a close ("QUIT" to FTP, or the logout command
appropriate for the remote system in the case of Telnet). When either
FTP or Telnet sees the incoming half of a TCP connection close, it
automatically responds by closing the outgoing half of the connection.
Close is more graceful than the "reset" command, in that it is
less likely to leave the remote TCP in a "half-open" state.
7.3.8. connect <interface> <callsign> [<digipeater> ... ]
Initiates a "vanilla" AX.25 session to the specified call sign
- 66 -
using the specified interface. Up to 7 optional digipeaters may be
given; note that the word "via" is NOT needed. Data sent on this
session goes out in conventional AX.25 packets with no upper layer pro-
tocol. The de-facto presentation standard format is used, in that
each packet holds one line of text, terminated by a carriage return. A
single AX.25 connection may be used for both terminal-to-terminal and
IP traffic, with the two types of data being automatically separated
by their AX.25 Level 3 Protocol IDs.
7.3.9. dir [<dirname>]
List the contents of the specified directory on the console. If no
argument is given, the current directory is listed.
7.3.10. disconnect [<session #>]
An alias for the "close" command (for the benefit of AX.25 users).
7.3.11. echo [accept|refuse]
Displays or changes the flag controlling client Telnet's response to a
remote WILL ECHO offer.
The Telnet presentation protocol specifies that in the absence of a
negotiated agreement to the contrary, neither end echoes data
received from the other. In this mode, a Telnet client session echoes
keyboard input locally and noth- ing is actually sent until a car-
riage return is typed. Local line editing is also performed: backspace
deletes the last character typed, while control-U deletes the entire
line.
When communicating from keyboard to keyboard the standard local echo
mode is used, so the setting of this parameter has no effect. However,
many timeshar- ing systems (e.g., UNIX) prefer to do their own echoing
of typed input. (This makes screen editors work right, among other
things). Such systems send a Tel- net WILL ECHO offer immediately upon
receiving an incoming Telnet connection request. If "echo accept" is
in effect, a client Telnet session will automati- cally return a DO ECHO
response. In this mode, local echoing and editing is turned off and
each key stroke is sent immediately (subject to the Nagle tinygram
algorithm in TCP). While this mode is just fine across an Ethernet, it
is clearly inefficient and painful across slow paths like packet
radio channels. Specifying "echo refuse" causes an incoming WILL ECHO
offer to be answered with a DONT ECHO; the client Telnet session
remains in the local echo mode. Sessions already in the remote echo
mode are unaffected. (Note: Berke- ley Unix has a bug in that it will
still echo input even after the client has refused the WILL ECHO offer.
To get around this problem, enter the "stty -echo" command to the
shell once you have logged in.)
7.3.12. eol [unix|standard]
Displays or changes Telnet's end-of-line behavior when in remote echo
mode. In standard mode, each key is sent as-is. In unix mode,
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carriage returns are translated to line feeds. This command is not
necessary with all UNIX sys- tems; use it only when you find
that a particular system responds to line feeds but not carriage
returns. Only Sun UNIX release 3.2 seems to exhibit this behavior;
later releases are fixed.
7.3.13. escape <char>
Without arguments, displays the current command-mode escape character in
hex. If given an argument, the first character becomes the new
escape character. (This command is not provided on the IBM-PC; on the
PC, the escape char is always F10.)
7.3.14. etherstat
Display 3-Com Ethernet controller statistics (if configured).
7.3.15. exit
Exit the "net" program and return to MS-DOS (or CP/M).
7.3.16. finger
For information on the Finger subsystem, see the information in the
advanced topics section of this manual.
7.3.17. ftp <hostid>
Open an FTP control channel to the specified remote host and enter
converse mode on the new session.
When in converse mode with an FTP server, everything typed on the con-
sole is first examined to see if it is a locally-known command. If
not, the line is passed intact to the remote server on the control chan-
nel. If it is one of the following commands, however, it is executed
locally. (Note that this generally involves other commands being sent to
the remote server on the control channel.) When actively transfer-
ring a file, the only acceptable command is "abort"; all other com-
mands will result in an error message. Responses from the remote
server are displayed directly on the screen.
7.3.17.1. abort
Aborts a get, put or dir operation in progress. When receiving a file,
abort simply resets the data connection; the next incoming data packet
will generate a TCP RST (reset) in response which will clear the remote
server. When send- ing a file, abort sends a premature end-of-file.
Note that in both cases abort will leave a partial copy of the file on
the destination machine, which must be removed manually if it is
unwanted. Abort is valid only when a transfer is in progress.
7.3.17.2. dir [<file>|<directory> [<localfile>]]
Without arguments, "dir" requests that a full directory listing of the
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remote server's current directory be sent to the terminal. If one argu-
ment is given, this is passed along in the LIST command; this can be a
specific file or sub- directory that is meaningful to the remote file
system. If two arguments are given, the second is taken as the local
file into which the directory listing should be put (instead of
being sent to the console). The PORT command is used before the LIST
command is sent.
7.3.17.3. get <remote_file> [<local_file>]
Asks the remote server to send the file specified in the first argument.
The second argument, if given, will be the name of the file on the
local machine; otherwise it will have the same name as on the remote
machine. The PORT and RETR commands are sent on the control channel.
7.3.17.4. ls [<file>|<directory> [<localfile>]]
ls is identical to the "dir" command except that the "NLST" command is
sent to the server instead of the "LIST" command. This results in
an abbreviated directory listing, i.e., one showing only the file names
themselves without any other information.
7.3.17.5. mkdir <remote_directory>
Creates a directory on the remote machine.
7.3.17.6. put <local_file> [<remote_file>]
Asks the remote server to accept data, creating the file named in the
first argument. The second argument, if given, will be the name of the
file on the remote machine; otherwise it will have the same name as on
the local machine. The PORT and STOR commands are sent on the control
channel.
7.3.17.7. rmdir <remote_directory>
Deletes a directory on the remote machine.
7.3.17.8. type [a|i|l<bytesize>]
Tells both the local client and remote server the type of file that is
to be transferred. The default is 'a', which means ASCII (i.e., a text
file). Type length lines of text in ASCII separated by cr/lf
sequences; in IMAGE mode, files are sent exactly as they appear in the
file system. ASCII mode should be used whenever transferring text
between dissimilar systems (e.g., UNIX and MS-DOS) because of their dif-
ferent end-of-line and/or end-of-file conventions. When exchanging text
files between machines of the same type, either mode will work but IMAGE
mode may be somewhat faster. Naturally, when exchanging raw binary
files (executables, compressed archives, etc) IMAGE mode must be used.
Type 'l' (logical byte size) is used when exchanging binary files with
remote servers having oddball word sizes (e.g., DECSYSTEM-10s and
20s). Locally it works exactly like IMAGE, except that it notifies the
remote system how large the byte size is. <bytesize> is typically 8.
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The type command sets the local transfer mode and generates the TYPE
command on the control channel.
7.3.18. help
Display a brief summary of top-level commands.
7.3.19. hostname [<name>]
Displays or sets the local host's name (an ASCII string such as "ka9q-
pc", NOT an IP address). Currently this is used only in the greeting
messages from the SMTP (mail) and FTP (file transfer) servers.
7.3.20. log [stop|<file>]
Without arguments, indicates whether server sessions are being
logged. If "stop" is given as the argument, logging is terminated (the
servers themselves are unaffected). If a file name is given as an argu-
ment, server session log entries will be appended to it.
7.3.21. ip
7.3.21.1. ip address [<hostid>]
Displays or sets the local IP address.
7.3.21.2. ip status
Displays Internet Protocol (IP) statistics, such as total packet
counts and error counters of various types. Also displays statistics
about the Internet Control Message Protocol (ICMP), including the number
of ICMP messages of each type sent or received.
7.3.21.3. ip ttl [<val>]
Displays or sets the default time-to-live value placed in each outgo-
ing IP datagram. This limits the number of switch hops the datagram
will be allowed to take. The idea is to bound the lifetime of the
packet should it become caught in a routing loop, so make the value
somewhat larger than the diameter of the network.
7.3.22. memstat
Displays the internal free memory list in the storage allocator.
7.3.23. mode <interface> [vc|datagram]
Controls the default transmission mode on the specified AX.25 inter-
face. In "datagram" mode, IP packets are encapsulated in AX.25 UI
frames and transmit- ted without any other link level mechanisms, such
as connections or ack- nowledgements.
In "vc" (virtual circuit) mode, IP packets are encapsulated in AX.25 I
frames and are acknowledged at the link level according to the AX.25
- 70 -
protocol. Link level connections are opened if necessary. With the
proper setting of the AX.25 T2 (acknowledgement delay) timer,
AX.25 acknowledgements can be pig- gybacked on I frames carrying other
IP datagrams (e.g., TCP level acknowledge- ments), thereby eliminating
the extra overhead ordinarily incurred by link level acknowledgments.
In both modes, ARP is used to map IP to AX.25 addresses. The defaults
can be overridden with the type-of-service (TOS) bits in the IP
header. Turning on the "reliability" bit causes I frames to be used,
while turning on the "low delay" bit uses UI frames. (The effect
of turning on both bits is undefined and subject to change).
In both modes, IP-level fragmentation is done if the datagram is larger
than the interface MTU. In virtual circuit mode, however, the result-
ing datagram (or fragments) is further fragmented at the AX.25 layer if
it (or they) are still larger than the AX.25 "paclen" parame-
ter. In AX.25 fragmentation, datagrams are broken into several I frames
and reassembled at the receiving end before being passed to IP. This
is preferable to IP fragmentation whenever possible because of decreased
overhead (the IP header isn't repeated in each fragment) and increased
robustness (a lost fragment is immediately retransmit- ted by the link
layer).
7.3.24. mulport [on|off]
The multiport switch software allows routing of frames between inter-
faces based on a table lookup. This provides the traditional "multi-port
digipeater" functionality.
There are two tables that you must build and place in the root direc-
tory. They are named DIGILIST and EXLIST. DIGILIST contains the digis
that are directly reachable from your switch. The file is a simple
ASCII text file containing the callsign of the digi and the interface
name of the port needed to reach it. The port name is the same name
you used in the attach statement for that port. Additionally there is a
special callsign "lan" that tells mulport which port feeds your LAN or
default port.
The file would look something like this:
kd4nc-1 ax1 # kd4nc-1 is a neighbor switch on the high speed
# link attached to ax1 wb4gqx-1 ax3 # wb4gqx-1 is a
neighbor digi on 145.01 (ax3) k4hal-1 ax2 # k4hal-1 is a neighbor
digi on 440 (ax2) lan ax0 # lan is a special name for the low
speed lan
# attached to the switch and is the default port
# used when mycall is the last call in the digi
# string.
The file EXLIST holds DESTINATION callsigns that do not obey the rules.
EXLIST is only for stations who would normally be expected to be on the
lan side but are operating off some other port instead. A couple of
reasons that this may be the case are that the station may be a PBBS
operating on the trunk to serve more than one lan.
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7.3.25. param <interface> [param]
Param invokes a device-specific control routine. On a KISS TNC
interface, this sends control packets to the TNC. Data bytes are
treated as decimal. For example, "param ax0 1 255" will set the keyup
timer (type field = 1) on the KISS TNC configured as ax0 to 2.55
seconds (255 x .01 sec). On a SLIP interface, the param command allows
the baud rate to be read (without arguments) or set. The implementa-
tion of this command for the various interface drivers is incomplete and
subject to change.
7.3.26. pwd [<dirname>]
An alias for the cd command.
7.3.27. record [<filename>|off]
Opens <filename> and appends to it all data received on the current
session. Data sent on the current session is also written into the file
except for Tel- net sessions in remote echo mode. The command "record
off" stops recording and closes the file. This command is not sup-
ported for FTP sessions.
7.3.28. reset [<session>]
If an argument is given, force a local reset (deletion) of the AX.25
(AXCB) or TCP Control Block (TCB) belonging to the specified session.
The argument is first checked for validity. If no argument is given,
the current session, if any, is used. This command should be used
with caution since it does not inform the remote end that the connection
no longer exists. (In TCP a reset (RST) message will be automati-
cally generated should the remote TCP send any- thing after a local
reset has been done. In AX.25 the DM message performs a similar
role. Both are used to get rid of a lingering half-open connection
after a remote system has crashed.)
7.3.29. route
route add <dest hostid>[/bits]|default <interface> [<gateway hostid>
[<metric>]]
route drop <dest hostid>
With no arguments, "route" displays the IP routing table. "route add"
adds an entry to the routing table, while "route drop" deletes an
existing entry. "route add" requires at least two more arguments, the
host id of the target destination and the local name of the interface
to which its packets should be sent. If the destination is not local,
the gateway's host id should also be specified. (If the interface is
a point-to-point link, then <gateway hostid> may be omitted even if the
target is non-local because this field is only used to determine the
gateway's link level address, if any. If the destination is directly
reachable, <gateway hostid> is also unnecessary since the destination
address is used to determine the interface link address).
- 72 -
The optional "/bits" suffix to the destination host id specifies how
many leading bits in the host id are to be considered significant in
the routing comparisons. If not specified, 32 bits (i.e., full signifi-
cance) is assumed. With this option, a single routing table entry
may refer to many hosts all sharing a common bit string prefix in their
IP addresses. For example, ARPA Class A, B and C networks would use
suffixes of /8, /16 and /24 respectively; the command
route add [44]/8 sl0 [44.64.0.2]
causes any IP addresses beginning with "44" in the first 8 bits to be
routed to [44.64.0.2]; the remaining 24 bits are "don't-cares".
When an IP address to be routed matches more than one entry in the
routing table, the entry with largest "bits" parameter (i.e., the
"best" match) is used. This allows individual hosts or blocks of hosts
to be exceptions to a more general rule for a larger block of hosts.
The special destination "default" is used to route datagrams to
addresses not in the routing table; it is equivalent to specifying a
/bits suffix of /0 to any destination hostid. Care must be taken with
default entries since two nodes with default entries pointing at
each other will route packets to unk- nown addresses back and forth in a
loop until their time-to-live (TTL) fields expire. (Routing loops
for specific addresses can also be created, but this is less likely to
occur accidentally).
"route drop" deletes an entry from the table. If a packet arrives
for the deleted address and a default route is in effect, it will be
used.
Here are some examples of using the route command:
# Route datagrams to IP address 44.0.0.3 to SLIP line #0.
# No gateway is needed because SLIP is point-to point.
route add [44.0.0.3] sl0
# Route all default traffic to the gateway on the local Ethernet
# with IP address [44.0.0.1]
route add default ec0 [44.0.0.1]
# The local Ethernet has an ARPA Class-C address assignment;
# route all IP addresses beginning with 192.4.8 to it
route add [192.4.8]/24 ec0
# Station with IP address [44.0.0.10] on local AX.25 channel
route add [44.0.0.10] ax0
7.3.30. session [<session #>]
Without arguments, displays the list of current sessions, including
session number, remote TCP or AX.25 address and the address of the TCP
or AX.25 control block. An asterisk (*) is shown next to the "current"
session; entering <cr> at this point will put you in converse mode
- 73 -
with that session. Entering a session number as an argument to the ses-
sion command will put you in converse mode with that session. If
the telnet server is enabled, the user is notified of an incoming
request and a session number is automatically assigned. The user
may then select the session normally to converse with the remote user as
though the session had been locally initiated.
7.3.31. shell
Suspends "net" and executes a sub shell ("command processor" under
MS-DOS). When the sub shell exits, net resumes (under MS-DOS, enter
the "exit" command). Note that background activity (FTP servers, etc)
is also suspended while the subshell executes.
7.3.32. smtp
7.3.32.1. smtp gateway [<hostid>]
Displays or sets the host to be used as a "smart" mail relay. Any mail
sent to a hostid not in the host table will instead be sent to the
gateway for forwarding.
7.3.32.2. smtp kick
Run through the outgoing mail queue and attempt to deliver any pending
mail. This command is periodically invoked by a timer whenever net is
running; this command allows the user to "kick" the mail system manu-
ally.
7.3.32.3. smtp maxclients [<val>]
Displays or sets the maximum number of simultaneous outgoing SMTP
sessions that will be allowed. The default is 10; reduce it if network
congestion is a problem.
7.3.32.4. smtp timer [<val>]
Displays or sets the interval, in seconds, between scans of the outbound
mail queue. For example, "smtp timer 600" will cause the system to check
for outgoing mail every 10 minutes and attempt to deliver anything it
finds, subject of course to the "maxclients" limit. Setting a value of
zero disables queue scanning altogether, note that this is the default!
This value is recommended for stand alone IP gateways that never han-
dle mail, since it saves wear and tear on the floppy disk drive.
7.3.32.5. smtp trace [<val>]
Displays or sets the trace flag in the SMTP client, allowing you to
watch SMTP's conversations as it delivers mail. Zero (the default)
disables trac- ing.
7.3.33. start
Starts the specified Internet server, allowing remote connection
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requests.
7.3.34. stop
Stops the specified Internet server, rejecting any further remote
connect requests. Existing connections are allow to complete normally.
7.3.35. tcp
7.3.35.1. tcp irtt [<val>]
Display or set the intial round trip time estimate, in seconds, to be
used for new TCP connections until they can measure and adapt to the
actual value. The default is 5 seconds. Increasing this when operating
over slow channels will avoid the flurry of retransmissions that would
otherwise occur as the smoothed estimate settles down at the correct
value. Note that this command should be given before servers are
started in order for it to have effect on incoming connections.
7.3.35.2. tcp kick <tcp_addr>
If there is data on the send queue of the specified tcb, this command
forces an immediate retransmission.
7.3.35.3. tcp mss [<size>]
Display or set the TCP Maximum Segment Size in bytes that will be sent
on all outgoing TCP connect request (SYN segments). This tells the
remote end the size of the largest segment (packet) it may send. Chang-
ing MSS affects only future connections; existing connections are
unaffected.
7.3.35.4. tcp reset <tcb_addr>
Deletes the TCP control block at the specified address.
7.3.35.5. tcp rtt <tcp_addr> <rtval>
Replaces the automatically computed round trip time in the specified tcb
with the rttval in milliseconds. This command is useful to speed up
recovery from a series of lost packets since it provides a manual bypass
around the normal backoff retransmission timing mechanisms.
7.3.35.6. tcp status [<tcb_addr>]
Without arguments, displays several TCP-level statistics, plus a sum-
mary of all existing TCP connections, including TCB address, send
and receive queue sizes, local and remote sockets, and connection state.
If <tcb_addr> is specified, a more detailed dump of the specified TCB
is generated, including send and receive sequence numbers and timer
information.
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7.3.35.7. tcp window [<val>]
Displays or sets the default receive window size in bytes to be used
by TCP when creating new connections. Existing connections are unaf-
fected.
7.3.36. telnet <hostid>
Creates a Telnet session to the specified host and enters converse mode.
7.3.37. trace [<interface> [<flags>]|allmode|cmdmode]
Controls packet tracing by the interface drivers. Specific bits enable
tracing of the various interfaces and the amount of information pro-
duced. Tracing is controlled on a per-interface basis; without argu-
ments, trace gives a list of all defined interfaces and their tracing
status. Output can be limited to a single interface by specifying it,
and the control flags can be change by specifying them as well.
The flags are given as a hexadecimal number which is interpreted as fol-
lows:
TIO
|||--- Enable tracing of output packets if 1, disable if 0
||---- Enable tracing of input packets if 1, disable if 0
|----- Controls type of tracing:
0 - Protocol headers are decoded, but data is not displayed
1 - Protocol headers are decoded, and data (but not the
headers themselves) are displayed as ASCII characters,
64 characters/line. Unprintable characters are displayed
as periods.
2 - Protocol headers are decoded, and the entire packet
(headers AND data) is also displayed in hexadecimal
and ASCII, 16 characters per line.
There is an additional option for tracing, that allows you to select
whether traced packets are always displayed, or only displayed when you
are in command mode. Having tracing only happen in command mode some-
times provides the right mix between "knowing what's going on", and
"keeping the garbage off the screen" while you're typing. To select
tracing all the time (the default mode), use 'trace allmode'. To res-
trict tracing to command mode, use 'trace cmdmode'.
7.3.38. udp status
Displays the status of all UDP receive queues.
7.3.39. upload [<filename>]
Opens <filename> and sends it on the current session as though it were
typed on the terminal. Valid only on AX.25 and Telnet sessions.
7.3.40. ?
Same as the "help" command.
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8. Appendices
8.1. Obtaining Current Bits
The KA9Q Internet software package is still evolving and growing. As a
result, we occasionally issue updates to the software that fix bugs
and/or update functionality. Announcements are always made to the USENET
news group rec.ham-radio.packet. They usually also show up on Com-
puserve within a day or two. There is never any charge for the software.
A small charge may exist for copying floppies if you want the bits on
disk, and of course you'll have to pay the long distance if you grab the
bits over the phone!
If several people are running the software in your area, get together
and decide on one person to get the new bits, then copy it around. We
won't mind.
8.1.1. Via FTP on the Internet
The most recent official release is usually available from the machine
WSMR-SIMTEL20.ARMY.MIL on the Internet. Use anonymous FTP, and look in
the directory PD3:<MISC.KA9Q-TCPIP>.
Beta-releases are often available on the machine LOUIE.UDEL.EDU, in the
directory tree rooted at pub/ka9q. Anonymous FTP's are allowed, but
unless you're working on the software, the bits on louie can be
"dangerous", as they often include incompletely implemented features,
and can have serious bugs. Caveat Emptor.
Various bits are also available from TOMCAT.GSFC.NASA.GOV, a machine
operated by Tom Clark W3IWI.
8.1.2. On PC Floppies
The Tucson Amateur Packet Radio association (TAPR) now provides floppy
copies of the software on 360k PC floppies, and can provide KISS ROMs
for various TNC's, at a nominal charge for duplication and shipping.
Contact TAPR for more information.
TAPR PO Box 12925 Tucson, AZ 85732 (602) 323-1710
8.1.2.1. WB3FFV's Phone BBS in the USA
Howard Leadmon, WB3FFV, has placed a BBS system on-line that is mainly
oriented towards the Amateur Community (but there is other stuff on-
line). Below is the information that is needed in order to access the
BBS via Telephone -or- TCP/IP.
System Name: WB3FFV
Login: bbs
Number: (301)-335-0858 -- 1200 & 2400 (Non-MNP)
Number: (301)-335-1955 -- 2400 (MNP), 9600 & 19200 (PEP)
Data Settings: 8 Bits, NO Parity, 1 Stop Bit
Times: 24hrs/365days (except for routine maintenance)
- 77 -
Software: XBBS (UNIX/Xenix Multiuser BBS)
IP Address: 44.60.0.1 {wb3ffv.ampr.org} [for FTP access on 145.550 mhz
ONLY]
Misc. Info: Machine is an 80386 computer running UNIX V.3.2 and
features 300+
meg of on-line storage. Most transfer protocols are avail-
able!!
Howard attempts to keep the latest and greatest HAM software on-line,
and encourages all to upload anything new that they come up with.
8.1.2.2. PA0GRI's Phone BBS in Holland
For those outside the USA, particularly in Europe, Gerard provides BBS
service and anonymous UUCP access to the machine 'gvdgpc'. He supports
Xmodem and Kermit on the BBS, at 1200/2400 baud, auto baud rate detect
by hitting a carriage return, using 8 bits, NO Parity, 1 Stop Bit. The
telephone number is 0031-70-119549.
For uucp, use login 'nuucp', with no password (you won't be prompted for
one). Request the file ~/FILES to get started. Gerard does a good job
of staying up to date via a link to the wb3ffv machine.
8.1.3. Gary Sanders' Phone BBS in the USA
Gary Sanders, N8EMR, runs a system called HBBS (Ham Bulletin board sys-
tem). The telephone number is 614-457-4227 (457-HBBS). The system is
online 24hrs a day and will accept 1200/2400 and 19.2k baud PEP, 8 bits
no parity, 1 stop bit.
Gary's system will be used to support topics of interest to Ham Radio
Operators, Short Wave Listeners, scanner listeners, and TVRO users.
Currently there are message and file upload/dowload sections for general
ham radio, packet radio, the KA9Q tcp software, SWL, and scanners.
There is also readonly access to Unix USENET and to the FIDO network
radio related newsgroups.
Access to the BBS files are available via FTP from n8emr [44.70.0.1].
The system is available via 144.97 in Central Ohio, or via the 220 and
446 packet network within Ohio.
8.1.4. Michael Broqvist in Sweden
Michael operates a BBS for the Gothenburg Amateur Club called the HamNet
Conference System. It operates at +46/31-30 35 25, 300-2400 baud.
Michael can be reached as sysop of Fidonet node 2:202/301, as
mibro@hamnet.se on the Internet, or via uucp as enea!hamnet.se!mibro.
He also updates the packet mailbox SK6SA in Gothenburg Sweden which is
reachable as 44.140.18.2.
- 78 -
8.2. The KISS Specification
8.3. The KISS Host to TNC Protocol
8.3.1. The Protocol Specification
8.3.1.1. Introduction
The purpose of the "Raw" (aka "KISS") TNC is to facilitate the use of
amateur packet radio controllers (TNCs) with host computers, par-
ticularly in the development of experimental protocols and multi-user
servers (e.g., "bulletin boards").
Current TNC software was written with human users in mind; unfor-
tunately, commands and responses well suited for human use are ill-
adapted for host computer use, and vice versa. This is especially true
for multi-user servers such as bulletin boards which must multiplex
data from several network connections across the single host/TNC link.
In addition, experimentation with new link level protocols is
greatly hampered because there may very well be no way at all to gen-
erate or receive frames in the desired format without reprogramming the
TNC.
The Raw TNC solves these problems by eliminating as much as possible
from the TNC software, giving the attached host complete control over
and access to the contents of the HDLC frames transmitted and received
over the air. The AX.25 protocol is removed entirely from the TNC, as
are all command interpreters and the like. The TNC simply converts
between synchronous HDLC, spoken on the half duplex radio channel,
and a special asynchronous, full duplex frame format spoken on the
host/TNC link. Every frame received on the HDLC link is passed
intact to the host once it has been translated to the asynchronous for-
mat; likewise, asynchronous frames from the host are transmitted on the
radio channel once they have been converted to HDLC format.
Of course, this means that the bulk of AX.25 (or another protocol) must
now be implemented on the host system. This is acceptable, however,
considering the greatly increased flexibility and reduced overall com-
plexity that comes from allowing the protocol to reside on the same
machine with the applications to which it is closely coupled.
8.3.1.2. Asynchtronous Frame Format
The "asynchronous packet protocol" spoken between the host and TNC is
very simple, since its only function is delimiting frames. Each frame
is both preceded and followed by a special FEND (frame end) character,
analogous to an HDLC flag. No CRC or checksum is provided.
The reason for both preceding and ending frames with FENDs is to improve
performance when there is noise on the asynch line. The FEND at the
beginning of a frame serves to "flush out" any accumulated garbage into
a separate frame (which will be discarded by the upper layer protocol)
instead of prepending it to an otherwise good frame. As with back-to-
back FLAGs in HDLC, two FEND characters in a row should not be
- 79 -
interpreted as delimiting an empty frame.
8.3.1.2.1. Transparency
Frames are sent in 8-bit binary; if an FEND ever appears in the data,
it is translated into the two byte sequence FESC TFEND (frame
escape, transposed frame end). Likewise, if the FESC character ever
appears in the user data, it is replaced with the two character
sequence FESC TFESC (frame escape, transposed frame escape).
As characters arrive at the receiver, they are appended to a buffer con-
taining the current frame. Receiving a FEND marks the end of the
current frame. Receipt of a FESC puts the receiver into "escaped
mode", which causes the receiver to translate a following TFESC or
TFEND back to FESC or FEND, respectively, before adding it to the
receive buffer and leaving escaped mode. (Receipt of any charac-
ter other than TFESC or TFEND while in escaped mode is an error; no
action is taken and frame assembly continues. A TFEND or TESC
received while not in escaped mode is treated as an ordinary data char-
acter.)
This procedure may seem somewhat complicated, but it is easy to imple-
ment and recovers quickly from errors. In particular, the FEND charac-
ter is never sent over the channel except as an actual end-of-frame
indication. This ensures that any intact frame (properly delimited
by FEND characters) will always be received properly regardless of the
starting state of the receiver or corruption of the preceding frame.
The special characters are:
FEND (frame end) 300 (octal)
FESC (frame escape) 333 (octal)
TFEND (transposed frame end) 334 (octal)
TFESC (transposed frame escape) 335 (octal)
(ARPA Internet hackers will recognize this protocol as identical to
SLIP, a popular method for sending IP datagrams across ordinary dialup
modems).
8.3.1.3. Control of the Raw TNC
Each asynchronous data frame sent to the TNC is converted back into
"pure" form and queued for transmission as a separate HDLC frame.
Although removing the human interface and the AX.25 protocol from the
TNC makes most existing TNC commands unnecessary (i.e., they become
host functions), the TNC is still responsible for keying the
transmitter's PTT line and deferring to other activity on the
radio channel. It is therefore necessary to allow the host to control a
few TNC parameters, namely the transmitter keyup delay and the
transmitter persistence variables.
It is therefore necessary to distinguish between command and data
frames on the host/TNC link. This is done by defining the first byte
of each asynchronous frame between host and TNC as a "type" indicator.
- 80 -
The following types are defined in frames to the TNC:
Type Function Comments
0 Data frame Rest of frame is data destined for HDLC channel
1 TXDELAY Second byte is TX keyup delay in 10 ms units
2 P Second byte is persistence parameter, p:
0: p = (0+1)/256, 255: p = (255+1)/256 = 1.0]
3 SLOTTIME Second byte is slot interval in 10 ms units
4 TXtail Second byte is time to hold up the TX after
the FCS has been sent (time allowed to send the
HDLC flag character; should be at least 2 for
1200 bps operation). In 10 ms units.
The following types are defined in frames to the host:
Type Function Comments
0 Data frame Rest of frame is data from the HDLC channel
(No other types are defined; in particular, there is no provision for
ack- nowledging data or command frames sent to the TNC.)
8.3.1.4. Persistence
The P and SLOTTIME parameters are used to implement true p-persistent
CSMA. This works as follows:
Whenever the host has queued data for transmission, the TNC begins mon-
itoring the carrier detect signal from the modem. It waits indefinitely
for this sig- nal to go inactive. Once the channel is clear, the TNC
generates a random number between 0 and 255. If this number is less
than or equal to P, the TNC asserts the transmitter PTT line, waits .01
* TXDELAY seconds, and transmits all frames in its queue. The TNC
then releases PTT and goes back to the idle state. If the random number
is greater than P, the TNC delays signal has gone active in the
meantime, the TNC again waits for it to clear before con- tinuing).
Note that P=255 means always transmit as soon as possible,
regardless of the random number.
The result is that the TNC waits for an exponentially-distributed
random interval after sensing that the channel has gone clear before
attempting to transmit. The idea here is that with proper tuning of the
parameters P and SLOTTIME, several stations with traffic to send are
much less likely to col- lide with each other when they simultaneously
see the channel go clear.
8.3.2. The TNC-2 Implementation
See the files included in the TNC-2 KISS Distribution.
- 81 -
8.3.3. The TNC-1 Implementation
See the files included in the TNC-1 KISS Distribution.
8.3.4. The VADCG/ASHBY Implementation
See the files included in the VADCG/ASHBY KISS Distribution.
8.3.5. The AEA Implemenation
All PK-232 units with WEFAX, and PC-87 units of a similar vintage, are
capable of KISS operation. See the installation instructions earlier in
this document for more information.
8.3.6. The Kantronics Implemenation
See your Kantronics TNC Documentation.
8.4. The FTP, Inc., Packet Driver Specification
The KA9Q TCP/IP package includes a driver that allows use of any network
interface that is provided with a "packet driver" that is compatible
with the "PC/TCP Version 1.08 Packet Driver Specification", by FTP
Software, Inc. The great benefit of the packet driver spec is that it
allows a manufacturer of a PC networking interface (an Ethernet card,
etc), to write one driver that can be loaded for use with a variety of
networking applications, including the KA9Q package.
For the benefit of potential packet driver authors, a copy of the spec
is included here. A prolific packet driver author is Russ Nelson, who
may be reached as nelson@sun.soe.clarkson.edu on the Internet. Many of
the drivers in use with the KA9Q package have been written or are being
maintained by Russ.
This section is derived from a public domain document created by FTP
Software, Inc. FTP Software is gratefully acknowledged for both
developing the spec, and allowing use of their specification here.
FTP Software, Inc.
P.O. Box 150
Kendall Sq. Branch
Boston, MA 02142
(617) 868-4878
Support of a hardware interface, or mention of an interface manufac-
turer, by the Packet Driver specification does not necessarily
indicate that the manufacturer endorses this specification.
8.4.1. Introduction and Motivation
This document describes the programming interface to PC/TCP packet
drivers. Packet drivers provide a simple, common programming
interface that allows multiple applications to share a network inter-
face at the data link level. The packet drivers demultiplex incoming
- 82 -
packets amongst the applications by using the network media type
field.
Different versions of PC/TCP exist for different network media (Eth-
ernet, 802.5 ring, serial lines), but through the use of the packet
driver, the actual brand or model of the network interface can be hid-
den from the application.
The packet driver provides calls to initiate access to a specific
packet type, to end access to it, to send a packet, to get statistics
on the network interface and to get information about the inter-
face.
Protocol implementations that use the packet driver can completely
coexist on a PC and can make use of one another's services, whereas mul-
tiple applications which do not use the driver do not coexist on one
machine properly. Through use of the packet driver, a user could run
TCP/IP, DECnet, and a proprietary protocol implementation such
as Banyan's, LifeNet's, Novell's or 3COM's without the diffi-
culties associated with preempting the network interface.
Applications which use the packet driver can also run on new network
hardware of the same class without being modified; only a new packet
driver need be supplied.
Two levels of packet drivers are described in this specifica-
tion. The first is the basic packet driver, which provides minimal
functionality but should be simple to implement and which uses
very few host resources. The basic driver provides operations to broad-
cast and receive packets. The second driver is the extended packet
driver, which is a superset of the basic driver. The extended driver
supports less commonly used functions of the network interface such
as multicast, and also gathers statistics on use of the interface
and makes these available to the application.
Functions which are available in only the extended packet driver are
noted as such in their descriptions. All basic packet driver func-
tions are available in the extended driver.
8.4.2. Identifying network interfaces
Network interfaces are named by a triplet of integers, <class,
type, number>. The first is the class of interface. The class tells
what kind of media the interface is for: DEC/Intel/Xerox/Ethernet,
IEEE 802.3 Ethernet, IEEE 802.5/Token Ring, ProNET-10, Broadband
Ethernet, Appletalk, serial line, etc.
The second number is the type of interface: this specifies a particular
instance of an interface supporting a class of medium. Interface
types for Ethernet might name these interfaces: 3COM 3C501 or
3C505, Interlan NI5010, Univation, BICC Data Networks ISOLAN,
Ungermann-Bass NIC, etc. Interface types for IEEE 802.5 might name
these interfaces: IBM Token Ring adapter, Proteon p1340, etc.
- 83 -
The last number is the interface number. If a machine is equipped
with more than one interface of a class and type, the interfaces must
be numbered to distinguish between them.
An appendix details constants for classes and types. The class of an
interface is an 8-bit integer, and its type is a 16 bit integer. Class
and type constants are managed by FTP Software. Contact FTP to
register a new class or type number.
The type 0xFFFF is a wildcard type which matches any interface
in the specified class. It is unnecessary to wildcard interface
numbers, as 0 will always correspond to the first interface of the
specified class and type.
This specification has no provision for the support of multiple
network interfaces (with similar or different characteristics)
via a single Packet Driver and associated interrupt. We feel that
this issue is best addressed by loading several Packet Drivers, one
per interface, with different interrupts (although all may
be included in a single TSR software module). Applications
software must check the class and type returned from a driver_info()
call already, to make sure that the Packet Driver is for the
correct media and packet format. This can easily be general-
ized by searching for another Packet Driver if the first is not of
the right kind.
8.4.3. Initiating driver operations
The packet driver is invoked via a software interrupt in the range 0x60
through 0x80. This document does not specify a particular interrupt,
but describes a mechanism for locating which interrupt
the driver uses. The interrupt must be configurable to avoid
conflicts with other pieces of software that also use software
interrupts. The program which installs the packet driver should
provide some mechanism for the user to specify the interrupt.
The handler for the interrupt is assumed to start with 3 bytes of
exectuable code; this can either be a 3-byte jump instruction, or
a 2-byte jump followed by a NOP (do not specify "jmp short" unless
you also specify an explicit NOP). This must be followed by the
null-terminated ASCII text string "PKT DRVR". To find the interrupt
being used by the driver, an application should scan through the
handlers for vectors 0x60 through 0x80 until it finds one with the
text string "PKT DRVR" in it.
8.4.4. Programming interface
All functions are accessed via the software interrupt determined
to be the driver's via the mechanism described earlier. On entry,
register AH contains the code of the function desired.
The handle is an arbitrary integer value associated with each
MAC-level demultiplexing type that has been established via the
access_type call. Internally to the packet driver, it will
- 84 -
probably be a pointer, or a table offset. The application calling
the packet driver cannot depend on it assuming any particular range,
or any other characteristics.
Note that some of the functions defined below are labelled as
extended driver functions. Because these are not required for
basic network operations, their implementation may be considered
optional. Programs wishing to use these functions should use the
driver_info() function to determine if they are available in a given
packet driver.
8.4.4.1. Entry Conditions
FTP Software applications which call the packet driver are coded in
Microsoft C and assembly language. All necessary registers are saved
by FTP's routines before the INT instruction to call the
packet driver is executed. Our current receiver() functions behave as
follows: DS and the flags are saved and restored. All other regis-
ters may be modified, and should be saved by the packet driver, if
necessary. Processor interrupts may be enabled while in the
upcall, but the upcall doesn't assume interrupts are disabled
on entry. On entry, receiver() switches to a local stack. Current FTP
Software receiver() routines may modify all registers except DS, so the
caller must save and restore any that must be preserved across the call.
Note that some older versions of PC/TCP may enable inter-
rupts during the upcall, and leave them enabled on return to the
Packet Driver.
8.4.4.2. Byte ordering
Developers should note that, on many networks and protocol families,
the byte-ordering of 16-bit quantities on the network is opposite
to the native byte-order of the PC. (802.5 Token Ring is an
exception). This means that DEC- Intel-Xerox ethertype values passed to
access_type() must be swapped (passed in network order). The IEEE
802.3 length field needs similar handling, and care should be taken
with packets passed to send_pkt(), so they are in the proper
order.
8.4.4.3. driver_info()
driver_info(handle) AH == 1 AL == FF
int handle; BX /* Optional */
error return:
carry flag set
error code DH
possible errors:
BAD_HANDLE /* older drivers only */
non-error return:
carry flag clear
version BX
- 85 -
class CH
type DX
number CL
name DS:SI
basic/extended AL
1 == basic, 2 == extended, FF == not installed
This function returns information about the interface. The version is
assumed to be an internal hardware driver identifier. In earlier
versions of this spec, the handle argument (which must have been
obtained via access_type()) was required. It is now optional, but
drivers developed according to versions of this spec previous to
1.07 may require it, so implementers should take care.
8.4.4.4. access_type()
int access_type(if_class, if_type, if_number, type, typelen,
receiver) AH == 2
int if_class; AL
int if_type; BX
int if_number; DL
char far *type; DS:SI
unsigned typelen; CX
int (far *receiver)(); ES:DI
error return:
carry flag set
error code DH
possible errors:
NO_CLASS
NO_TYPE
NO_NUMBER
BAD_TYPE
NO_SPACE
TYPE_INUSE
non-error return:
carry flag clear
handle AX
receiver call:
(*receiver)(handle, flag, len [, buffer])
int handle; BX
int flag; AX
unsigned len; CX
if AX == 1,
char far *buffer; DS:SI
Initiates access to packets of the specified type. The argument
type is a pointer to a packet type specification. The argument
typelen is the length in bytes of the type field. The argument
receiver is a pointer to a subroutine which is called when a
packet is received. If the typelen argument is 0, this indicates that
the caller wants to match all packets (match all requests may be
- 86 -
refused by packet drivers developed to conform to versions of
this spec previous to 1.07).
When a packet is received, receiver is called twice by the packet
driver. The first time is to request a buffer from the application
to copy the packet into. AX == 0 on this call. The application
should return a pointer to the buffer in ES:DI. If the application has
no buffers, it may return 0:0 in ES:DI, and the driver should
throw away the packet and not perform the second call.
It is important that the packet length (CX) be valid on the AX == 0
call, so that the receiver can allocate a buffer of the proper size.
This length (as well as the copy performed prior to the AX == 1 call)
must include the Ethernet header and all received data, but not the
trailing checksum.
On the second call, AX == 1. This call indicates that the copy has
been completed, and the application may do as it wishes with the
buffer. The buffer that the packet was copied into is pointed to by
DS:SI.
8.4.4.5. release_type()
int release_type(handle) AH == 3
int handle; BX
error return:
carry flag set
error code DH
possible errors:
BAD_HANDLE
non-error return:
carry flag clear
This function ends access to packets associated with a handle
returned by access_type(). The handle is no longer valid.
8.4.4.6. send_pkt()
int send_pkt(buffer, length) AH == 4
char far *buffer; DS:SI
unsigned length; CX
error return:
carry flag set
error code DH
possible errors:
CANT_SEND
non-error return:
carry flag clear
Transmits length bytes of data, starting at buffer. The application
- 87 -
must supply the entire packet, including local network headers. Any
MAC or LLC information in use for packet demultiplexing (e.g. the
DEC-Intel-Xerox Ethertype) must be filled in by the application as
well. This cannot be performed by the driver, as no handle is specified
in a call to the send_packet() function.
8.4.4.7. terminate()
terminate(handle) AH == 5
int handle; BX
error return:
carry flag set
error code DH
possible errors:
BAD_HANDLE
CANT_TERMINATE
non-error return:
carry flag clear
Terminates the driver associated with handle. If possible, the driver
will exit and allow MS-DOS to reclaim the memory it was using.
8.4.4.8. get_address()
get_address(handle, buf, len) AH == 6
int handle; BX
char far *buf; ES:DI
int len; CX
error return:
carry flag set
error code DH
possible errors:
BAD_HANDLE
NO_SPACE
non-error return:
carry flag clear
length CX
Copies the local net address associated with handle into buf. The
buffer buf is len bytes long. The actual number of bytes copied is
returned in CX. If the NO_SPACE error is returned, this indicates
that len was insufficient to hold the local net address.
8.4.4.9. reset_interface()
reset_interface(handle) AH == 7
int handle; BX
error return:
carry flag set
- 88 -
error code DH
possible errors:
BAD_HANDLE
non-error return:
carry flag clear
Resets the interface associated with handle to a known state,
aborting any transmits in process and reinitializing the receiver. This
call has been included primarily for circumstances where a high-
level protocol has detected what it thinks may be an interface
failure or hang. If the packet driver implementer has a high level
of confidence in the hardware, or the action would seriously disrupt
other users of the interface, this can be treated as a no-op.
8.4.4.10. set_rcv_mode()
extended driver function
set_rcv_mode(handle, mode) AH == 20
int handle; BX
int mode; CX
error return:
carry flag set
error code DH
possible errors:
BAD_HANDLE
BAD_MODE
non-error return:
carry flag clear
Sets the receive mode on the interface associated with handle. The
following values are accepted for mode:
mode meaning
1 turn off receiver
2 receive only packets sent to this interface
3 mode 2 plus broadcast packets
4 mode 3 plus limited multicast packets
5 mode 3 plus all multicast packets
6 all packets
Note that not all interfaces support all modes. The receive mode
affects all packets received by this interface, not just packets
associated with the handle argument. See the extended driver
functions get_multicast_list() and set_multicast_list() for
programming "perfect filters" to receive specific multicast addresses.
Note that mode 3 is the default, and if the set_rcv_mode() function
is not implemented, mode 3 is assumed to be in force as long as
any handles are open (from the first access_type() to the last
release_type()).
- 89 -
8.4.4.11. get_rcv_mode()
extended driver function get_rcv_mode(handle, mode) AH == 21
int handle; BX
error return:
carry flag set
error code DH
possible errors:
BAD_HANDLE
non-error return:
carry flag clear
mode AX
Returns the current receive mode of the interface associated with han-
dle.
8.4.4.12. set_multicast_list()
extended driver function set_multicast_list(addrlst, len)
AH == 22
char far *addrlst; ES:DI
int len; CX
error return:
carry flag set
error code DH
possible errors:
NO_MULTICAST
NO_SPACE
BAD_ADDRESS
non-error return:
carry flag clear
The addrlst argument is assumed to point to an len-byte buffer
containing a number of multicast addresses. BAD_ADDRESS is
returned if len modulo the size of an address is not equal to 0, or the
data is unacceptable for some reason. NO_SPACE is returned (and no
addresses are set) if there are more addresses than the
hardware supports directly.
The recommended procedure for setting multicast addresses is to issue a
get_multicast_list(), copy the information to a local buffer, add
any addresses desired, and issue a set_multicast_list(). This
should be reversed when the application exits. If the
set_multicast_list() fails due to NO_SPACE, use set_rcv_mode() to set
mode 5 instead.
8.4.4.13. get_multicast_list()
extended driver function get_multicast_list() AH == 23
- 90 -
error return:
carry flag set
error code DH
possible errors:
NO_MULTICAST
non-error return:
carry flag clear
char far *addrlst; ES:DI
int len; CX
On a successful return, addrlst points to len bytes of multicast
addresses currently in use. The application program must not modify
this information in-place.
8.4.4.14. get_statistics()
extended driver function get_statistics(handle) AH == 24
int handle; BX
error return:
carry flag set
error code DH
possible errors:
BAD_HANDLE
non-error return:
carry flag clear
char far *stats; DS:SI
statistics structure:
field byte length
packets in 4
packets out 4
bytes in 4
bytes out 4
errors in 4
errors out 4
packets dropped 4
Returns a pointer to a statistics structure for this handle.
8.4.4.15. set_address()
extended driver function set_address(addr, len) AH == 25
char far *addr; ES:DI
int len; CX
error return:
carry flag set
error code DH
possible errors:
CANT_SET
BAD_ADDRESS
- 91 -
non-error return:
carry flag clear
length CX
This call is used when the application or protocol stack needs to
use a specific LAN address. For instance, DECnet protocols on Eth-
ernet encode the protocol address in the Ethernet address, requir-
ing that it be set when the protocol stack is loaded. A BAD_ADDRESS
error indicates that the Packet Driver doesn't like the len (too
short or too long), or the data itself. Note that packet drivers
should refuse to change the address (with a CANT_SET error) if more
than one handle is open (lest it be changed out from under
another protocol stack).
8.4.5. Interface classes and types
The following are defined as network interface classes, with their
individual types listed immediately following the class.
DEC/Intel/Xerox "Bluebook" Ethernet 1
3COM 3C500/3C501 1 3COM 3C505 2 MICOM-
Interlan NI5010 3 BICC Data Networks 4110 4 BICC Data Net-
works 4117 5 MICOM-Interlan NP600 6 Ungermann-Bass PC-
NIC 8 Univation NC-516 9 TRW PC-2000 10
MICOM-Interlan NI5210 11 3COM 3C503 12 3COM
3C523 13 Western Digital WD8003 14 Spider Sys-
tems S4 15 Torus Frame Level 16 10NET Communica-
tions 17 Gateway PC-bus 18 Gateway AT-
bus 19 Gateway MCA-bus 20 IMC
PCnic 21 IMC PCnic II 22 IMC PCnic
8bit 23
ProNET-10 2
Proteon p1300 1
IEEE 802.5/ProNET-4 3
IBM Token ring adapter 1
Proteon p1340 2
Proteon p1344 3
Gateway PC-bus 4
Gateway AT-bus 5
Gateway MCA-bus 6
Omninet 4
Appletalk 5
Serial line 6
Starlan 7 (NOTE: subsumed by Ethernet)
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ArcNet 8
Datapoint RIM 1
AX.25 9
KISS 10
IEEE 802.3 w/802.2 hdrs 11
Types as given under DIX Ethernet, See Appendix D.
8.4.6. Function call numbers
The following numbers are used to specify which operation the packet
driver should perform. The number is stored in register AH on call to
the packet driver.
driver_info 1
access_type 2
release_type 3
send_pkt 4
terminate 5
get_address 6
reset_interface 7
*set_rcv_mode 20
*get_rcv_mode 21
*set_multicast_list 22
*get_multicast_list 23
*get_statistics 24
*set_address 25
* indicates an extended packet driver function
8.4.7. Error codes
Packet driver calls indicate error by setting the carry flag on return.
The error code is returned in register DH (a register not used
to pass values to functions must be used to return the error code).
The following error codes are defined:
1 BAD_HANDLE invalid handle number
2 NO_CLASS no interfaces of specified class found
3 NO_TYPE no interfaces of specified type found
4 NO_NUMBER no interfaces of specified number found
5 BAD_TYPE bad packet type specified
6 NO_MULTICAST this interface does not support
multicast
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7 CANT_TERMINATE this packet driver cannot terminate
8 BAD_MODE an invalid receiver mode was specified
9 NO_SPACE operation failed because of insufficient
space
10 TYPE_INUSE the type had previously been accessed,
and not released.
11 BAD_COMMAND the command was out of range, or not
implemented
12 CANT_SEND the packet couldn't be sent (usually
hardware error)
13 CANT_SET hardware address couldn't be changed
(more than 1 handle open)
14 BAD_ADDRESS hardware address has bad length or
format
8.4.8. 802.3 vs. Blue Book Ethernet
One weakness of the present specification is that there is no provi-
sion for simultaneous support of 802.3 and Blue Book (the old DEC-
Intel-Xerox standard) Ethernet headers via a single Packet Driver
(as defined by its interrupt). The problem is that the Ethertype
of Blue Book packets is in bytes 12 and 13 of the header,
and in 802.3 the corresponding bytes are interpreted as a length.
In 802.3, the field which would appear to be most useful to begin the
type check in is the 802.2 header, starting at byte 14.
This is only a problem on Ethernet and variants (e.g. Star-
lan), where 802.3 headers and Blue Book headers are likely to need
co-exist for many years to come.
One solution is to redefine class 1 as Blue Book Ethernet, and
define a parallel class for 802.3 with 802.2 packet headers. This
requires that a 2nd Packet Driver (as defined by its interrupt)
be implemented where it is necessary to handle both kinds
of packets, although they could both be part of the same TSR
module.
As of this draft, class 11 has been assigned to 802.3 using 802.2
headers, to implement the above.
Note: According to this scheme, an application wishing to receive IP
encapsulated per RFC 1042 would specify an typelen argument of 8,
and type would point to:
char iee_ip[] = {0xAA, 0xAA, 3, 0, 0, 0, 0x08, 0x00};
8.5. Information for Software Developers
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8.6. Technical Information for Client/Server Developers
First things first. The program has been tested out with the Turbo C
2.0 compiler under MS-Dos, the HP-UX 5.21 and 6.2 compilers, the Micro-
port 286 compiler, and the Mark Williams compiler on the Atari ST.
There is a known problem compiling under Aztec C 4.10d on the PC, if
someone can figure out what is going wrong it would be appreciated.
With that out of the way...
This section describes the "guts" of the Internet package for the bene-
fit of programmers who wish to write their own applications, or
adapt the code to different hardware environments. Potential application
developers should consider strongly writing new applications for the NOS
version of the package, which is currently in development. Contact Phil
Karn KA9Q or Bdale Garbee N3EUA for more information. There will *not*
be another release of the software based on the internal structure used
through this release.
The code as distributed includes both the functions of an IP packet
switch and an end-host system, including several servers. The imple-
mentation is highly modular, however. For example, if one wants to build
a dedicated packet switch without any local applications, the various
applications and the TCP and UDP modules may easily be omitted to save
space.
The package allows multiple simultaneous applications, each supporting
multi- ple simultaneous users, each using TCP and/or UDP. The only
limit is memory space, which is getting quite tight on the 820; the C
compiler for the IBM PC seems to generate much more compact code
(typically 1/2 as large as for the Z-80) so the PC seems more promising
as a large-scale server.
8.6.1. Data Structures
To increase portability, the pseudo-types "int16" and "int32" are used
to mean an unsigned 16-bit integer and a signed 32-bit integer,
respectively. Ordi- narily these types are defined in machdep.h to be
"unsigned int" and "long".
The various modules pass data in chained structures called mbufs,
with the following format:
struct mbuf {
struct mbuf *next; /* Link mbufs belonging to single packets */
struct mbuf *anext; /* Link packets on queues */
char *data; /* Ptr to start of actual data in buffer */
int16 cnt; /* Length of data in buffer */ };
Although somewhat cumbersome to work with, mbufs make it possible to
avoid memory-to-memory copies that limit performance. For example, when
user data is transmitted it must first traverse several protocol layers
before reaching the transmitter hardware. With mbufs, each layer adds
its protocol header by allo- cating an mbuf and linking it to the head
of the mbuf "chain" given it by the higher layer, thus avoiding several
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copy operations.
A number of primitives operating on mbufs are available in mbuf.c. The
user may create, fill, empty and free mbufs himself with the
alloc_mbuf and free_mbuf primitives, or at the cost of a single memory-
to-memory copy he he may use the more convenient qdata() and dqdata()
primitives.
8.6.2. Timer Services
TCP and IP require timers. A timer package is included, so the user
must arrange to call the single entry point "tick" on a regular basis.
The constant MSPTICK in timer.h should be defined as the interval
between ticks in milliseconds. One second resolution is adequate.
Since it can trigger a considerable amount of activity, including
upcalls to user level, "tick" should not be called from an interrupt
handler. A clock interrupt should set a flag which will then cause
"tick" to be called at user level.
8.6.3. Internet Type-of-Service
One of the features of the Internet is the ability to specify pre-
cedence (i.e., priority) on a per-datagram basis. There are 8 levels
of precedence, with the bottom 6 defined by the DoD as Routine, Prior-
ity, Immediate, Flash, Flash Override and CRITICAL. (Two more are
available for internal network functions). For amateur use we can use
the lower four as Routine, Welfare, Priority and Emergency. Three
more bits specify class of service, indicating that especially high
reliability, high throughput or low delay is needed for this connec-
tion. Constants for this field are defined in internet.h.
8.6.4. The Internet Protocol Implementation.
While the user does not ordinarily see this level directly, it is
described here for sake of completeness. Readers interested only in the
interfaces seen by the applications programmer should skip to the TCP
and UDP sections.
The IP implementation consists of three major functions: ip_route,
ip_send and ip_recv.
8.6.5. IP Gateway (Packet Router) Support
The first, ip_route, is the IP packet switch. It takes a single argu-
ment, a pointer to the mbuf containing the IP datagram:
void
ip_route(bp,rxbroadcast)
struct mbuf *bp; /* Datagram pointer */
int rxbroadcast; /* Don't forward */
All IP datagrams, coming or going, pass through this function. After
option processing, if any, the datagram's destination address is
extracted. If it corresponds to the local host, it is "kicked upstairs"
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to the upper half of IP and thence to the appropriate protocol module.
Otherwise, an internal routing table consulted to determine where the
datagram should be forwarded. The routing table uses hashing
keyed on IP destination addresses, called "tar- gets". If the target
address is not found, a special "default" entry, if available, is
used. If a default entry is not available either, an ICMP "Des- tination
Unreachable" message containing the offending IP header is returned to
the sender.
The "rxbroadcast" flag is used to prevent forwarding of broadcast pack-
ets, a practice which might otherwise result in spectacular routing
loops. Any subnet interface driver receiving a packet addressed to the
broadcast address within that subnet MUST set this flag. All other
packets (including locally ori- ginated packets) should have "rxbroad-
cast" set to zero.
ip_route ignores the IP destination address in broadcast packets, pass-
ing them up to the appropriate higher level protocol which is also made
aware of their broadcast nature. (TCP and ICMP ignore them; only UDP can
accept them).
Entries are added to the IP routing table with the rt_add function:
int rt_add(target,gateway,metric,interface) int32 target;
/* IP address of target */ int32 gateway; /* IP addr of
gateway to reach this target */ int metric; /*
"cost" metric, for routing decisions */ struct interface *interface;
/* device interface structure */
"target" is the IP address of the destination; it becomes the hash
index key for subsequent packet destination address lookups. If target
== 0, the default entry is modified. "metric" is simply stored in the
table; it is available for routing cost calculations when an
automatic routing protocol is written. "interface" is the address of a
control structure for the particular device to which the datagram
should be sent; it is defined in the section "IP Inter- faces".
rt_add returns 0 on success, -1 on failure (e.g., out of memory).
To remove an entry from the routing table, only the target address
need be specified to the rt_drop call:
int
rt_drop(target)
int32 target;
rt_drop returns 0 on success, -1 if the target could not be found.
8.6.6. IP Interfaces
Every lower level interface used to transmit IP datagrams must have an
"inter- face" structure, defined as follows:
/* Interface control structure */
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struct interface {
struct interface *next; /* Linked list pointer */
char *name; /* Ascii string with interface name */
int16 mtu; /* Maximum transmission unit size */
int (*send)(); /* Routine to call to send datagram */
int (*output)(); /* Routine to call to send raw packet */
int (*recv)(); /* Routine to kick to process input */
int (*stop)(); /* Routine to call before detaching */
int16 dev; /* Subdevice number to pass to send */
int16 flags; /* State of interface */
#define IF_ACTIVE 0x01
#define IF_BROADCAST 0x04 /* Interface is capable of broadcasting
*/ };
Part of the interface structure is for the private use of the device
driver. "dev" is used to distinguish between one of several identical
devices (e.g., serial links or radio channels) that might share the same
send routine.
A pointer to this structure kept in the routing table. Two fields
in the interface structure are examined by ip_route: "mtu" and
"send". The maximum transmission unit size represents the largest
datagram that this device can handle; ip_route will do IP-level frag-
mentation as required to meet this limit before calling "send", the
function to queue datagrams on this interface. "send" is called as
follows:
(*send)(bp,interface,gateway,precedence,delay,throughput,reliability)
struct mbuf *bp; /* Pointer to datagram */
struct interface *interface; /* Interface structure */
int32 gateway; /* IP address of gateway */
char precedence; /* TOS bits from IP header */
char delay;
char throughput;
char reliability;
The "interface" and "gateway" arguments are kept in the routing
table and passed on each call to the send routine. The interface
pointer is passed again because several interfaces might share the same
output driver (e.g., several identical physical channels). "gateway"
is the IP address of the neighboring IP gateway on the other end of the
link; if a link-level address is required, the send routine must
map this address either dynamically (e.g., with the Address Resolution
Protocol, ARP) or with a static lookup table. If the link is point-
to-point, link-level addresses are unnecessary, and the send routine can
therefore ignore the gateway address.
The Internet Type-of-Service (TOS) bits are passed to the interface
driver as separate arguments. If tradeoffs exist within the subnet
between these various classes of service, the driver may use these argu-
ments to control them (e.g., optional use of link level acknowledg-
ments, priority queuing, etc.)
It is expected that the send routine will put a link level header on the
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front of the packet, add it an internal output queue, start output (if
not already active) and return. It must NOT busy-wait for completion
(unless it is a very fast device, e.g., Ethernet) since that blocks the
entire system.
Any interface that uses ARP must also provide an "output" routine. It
is a lower level entry point that allows the caller to specify the
fields in the link header. ARP uses it to broadcast a request for a
given IP address. It may be the same routine used internally by the
driver to send IP datagrams once the link level fields have been deter-
mined. It is called as follows:
(*output)(interface,dest,src,type,bp)
struct interface *interface; /* Pointer to interface structure */
char dest[]; /* Link level destination address */
char src[]; /* Link level source address */
int16 type; /* Protocol type field for link level
*/
struct mbuf *bp; /* Data field (IP datagram) */
8.6.7. IP Host Support
All of the modules described thus far are required in all systems.
However, the routines that follow are necessary only if the sys-
tem is to support higher-level applications. In a standalone IP gateway
(packet switch) without servers or clients, the following modules (IP
user level, TCP and UDP) may be omitted to allow additional space for
buffering; define the flag GWONLY when compiling iproute.c to avoid
referencing the user level half of IP.
The following function is called by iproute() whenever a datagram
arrives that is addressed to the local system.
void
ip_recv(bp,rxbroadcast)
struct mbuf *bp; /* Datagram */
char rxbroadcast; /* Incoming broadcast */
ip_recv reassembles IP datagram fragments, if necessary, and calls the
input function of the next layer protocol (e.g., tcp_input,
udp_input) with the appropriate arguments, as follows:
(*protrecv)(bp,protocol,source,dest,tos,length,rxbroadcast);
struct mbuf *bp; /* Pointer to packet minus IP header */
char protocol; /* IP protocol ID */
int32 source; /* IP address of sender */
int32 dest; /* IP address of destination (i.e,. us) */
char tos; /* IP type-of-service field in datagram */
int16 length; /* Length of datagram minus IP header */
char rxbroadcast; /* Incoming broadcast */
The list of protocols is contained in a switch() statement in the
ip_recv function. If the protocol is unsupported, an ICMP Protocol
Unreachable message is returned to the sender unless the packet came in
- 99 -
as a broadcast. Higher level protocols such as TCP and UDP use the
ip_send routine to generate IP datagrams. The arguments to ip_send
correspond directly to fields in the IP header, which is generated and
put in front of the user's data before being handed to ip_route:
ip_send(source,dest,protocol,tos,ttl,bp,length,id,df)
int32 source; /* source address */
int32 dest; /* Destination address */
char protocol; /* Protocol */
char tos; /* Type of service */
char ttl; /* Time-to-live */
struct mbuf *bp; /* Data portion of datagram */
int16 length; /* Optional length of data portion */
int16 id; /* Optional identification */
char df; /* Don't-fragment flag */
This interface is modeled very closely after the example given on page
32 of RFC-791. Zeros may be passed for id or ttl, and system defaults
will be pro- vided. If zero is passed for length, it will be calculated
automatically.
8.6.8. The Transmission Control Protocol (TCP)
A TCP connection is uniquely identified by the concatenation of
local and remote "sockets". In turn, a socket consists of a host
address (a 32-bit integer) and a TCP port (a 16-bit integer), defined by
the C structure
struct socket {
long address; /* 32-bit IP address */
short port; /*16-bit TCP port */
};
It is therefore possible to have several simultaneous but distinct con-
nections to the same port on a given machine, as long as the remote
sockets are dis- tinct. Port numbers are assigned either through mutual
agreement, or more com- monly when a "standard" service is involved,
as a "well known port" number. For example, to obtain standard
remote login service using the TELNET presentation-layer protocol,
by convention you initiate a connection to TCP port 23; to send mail
using the Simple Mail Transfer Protocol (SMTP) you con- nect to port
25. ARPA maintains port number lists and periodically publishes them;
the latest revision is RFC-960, "Assigned Numbers". They will also
assign port numbers to a new application on request if it appears to
be of general interest.
TCP connections are best modeled as a pair of one-way paths (one in
each direction) rather than single full-duplex paths. A TCP "close"
really means "I have no more data to send". Station A may close its path
to station B leaving the reverse path from B to A unaffected; B
may continue to send data to A indefinitely until it too closes its half
of the connection. Even after a user initiates a close, TCP contin-
ues to retransmit any unacknowledged data if necessary to ensure that it
reaches the other end. This is known as "graceful close" and greatly
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simplifies certain applications such as FTP.
This package is written as a "module" intended to be compiled and linked
with the application(s) so that they can be run as one program on the
same machine. This greatly simplifies the user/TCP interface, which
becomes just a set of internal subroutine calls on a single
machine. The internal TCP state (e.g., the address of the remote
station) is easily accessed. Reliability is improved, since any
hardware failure that kills TCP will likely take its applications
with it anyway. Only IP datagrams flow out of the machine across
hardware interfaces (such as asynch RS-232 ports or whatever else is
avail- able) so hardware flow control or complicated host/front-end
protocols are unnecessary.
The TCP supports five basic operations on a connection: open_tcp,
send_tcp, receive_tcp, close_tcp and del_tcp. A sixth, state_tcp, is
provided mainly for debugging. Since this TCP module cannot assume the
presence of a sleep/wakeup facility from the underlying operating sys-
tem, functions that would ordinarily block (e.g., recv_tcp when no data
is available) instead set net_error to the constant EWOULDBLK and
immediately return -1. Asynchronous notification of events such as data
arrival can be obtained through the upcall facility described
earlier.
Each TCP function is summarized in the following section in the form
of C declarations and descriptions of each argument.
int net_error;
This global variable stores the specific cause of an error from one of
the TCP or UDP functions. All functions returning integers (i.e., all
except open_tcp) return -1 in the event of an error, and net_error
should be examined to determine the cause. The possible errors are
defined as constants in the header file netuser.h.
/* Open a TCP connection */
struct tcb *
open_tcp(lsocket,fsocket,mode,window,r_upcall,t_upcall,s_upcall,tos,user)
struct socket *lsocket; /* Local socket */
struct socket *fsocket; /* Remote socket */
int mode; /* Active/passive/server */
int16 window; /* Receive window (and send buffer) sizes */
void (*r_upcall)(); /* Function to call when data arrives */
void (*t_upcall)(); /* Function to call when ok to send more data
*/
void (*s_upcall)(); /* Function to call when connection state
changes */
char tos; /* Internet Type-of-Service */
int *user; /* Pointer for convenience of user */
"lsocket" and "fsocket" are pointers to the local and foreign sockets,
respec- tively.
"mode" may take on three values, all defined in net.user.h. If
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mode is TCP_PASSIVE, no packets are sent, but a TCP control block is
created that will accept a subsequent active open from another TCP. If a
specific foreign socket is passed to a passive open, then connect
requests from any other foreign socket will be rejected. If the foreign
socket fields are set to zero, or if fsocket is NULLSOCK, then
connect requests from any foreign socket will be accepted. If mode is
TCP_ACTIVE, TCP will initiate a connection to a remote socket that
must already have been created in the LISTEN state by its client. The
foreign socket must be completely specified in an active open. When
mode is TCP_SERVER, open_tcp behaves as though TCP_PASSIVE was given
except that an internal "clone" flag is set. When a connection request
comes in, a fresh copy of the TCP control block is created and the
original is left intact. This allows multiple sessions to exist simul-
taneously; if TCP_PASSIVE were used instead only the first connect
request would be accepted.
"r_upcall", "t_upcall" and "s_upcall" provide optional upcall or
pseudo- interrupt mechanisms useful when running in a non operating
system environ- ment. Each of the three arguments, if non-NULL, is
taken as the address of a user-supplied function to call when receive
data arrives, transmit queue space becomes available, or the connection
state changes. The three functions are called with the following
arguments:
(*r_upcall)(tcb,count); /* count == number of bytes in receive queue */
(*t_upcall)(tcb,avail); /* avail == space available in send queue */
(*s_upcall)(tcb,oldstate,newstate);
Note: whenever a single event invokes more than one upcall the order in
which the upcalls are made is not strictly defined. In general, though,
the Principle of Least Astonishment is followed. E.g., when entering
the ESTABLISHED state, the state change upcall is invoked first, fol-
lowed by the transmit upcall. When an incoming segment contains
both data and FIN, the receive upcall is invoked first, followed by
the state change to CLOSE_WAIT state. In this case, the user may inter-
pret this state change as a "end of file" indicator.
"tos" is the Internet type-of-service field. This parameter is passed
along to IP and is included in every datagram. The actual precedence
value used is the higher of the two specified in the corresponding pair
of open_tcp calls.
open_tcp returns a pointer to an internal Transmission Control Block
(tcb). This "magic cookie" must be passed back as the first argument to
all other TCP calls. In event of error, the NULL pointer (0) is returned
and net_error is set to the reason for the error.
The only limit on the number of TCBs that may exist at any time
(i.e., the number of simultaneous connections) is the amount of
free memory on the machine. Each TCB on a 16-bit processor currently
takes up 111 bytes; addi- tional memory is consumed and freed
dynamically as needed to buffer send and receive data. Deleting a TCB
(see the del_tcp() call) reclaims its space.
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/* Send data on a TCP connection */
int
send_tcp(tcb,bp)
struct tcb *tcb; /* TCB pointer */
struct mbuf *bp; /* Pointer to user's data mbufs */
"tcb" is the pointer returned by the open_tcp() call. "bp" points
to the user's mbuf with data to be sent. After being passed to
send_tcp, the user must no longer access the data buffer. TCP uses posi-
tive acknowledgments with retransmission to ensure in-order delivery,
but this is largely invisible to the user. Once the remote TCP has ack-
nowledged the data, the buffer will be freed automatically.
TCP does not enforce a limit in the number of bytes that may be
queued for transmission, but it is recommended that the application
not send any more than the amount passed as "cnt" in the transmitter
upcall. The package uses shared, dynamically allocated buffers, and
it is entirely possible for a mis- behaving user task to run the system
out of buffers.
/* Receive data on a TCP connection */
int
recv_tcp(tcb,bp,cnt)
struct tcb *tcb;
struct mbuf **bp;
int16 cnt;
recv_tcp() passes back through bp a pointer to an mbuf chain contain-
ing any available receive data, up to a maximum of "cnt" bytes. The
actual number of bytes received (the lesser of "cnt" and the number
pending on the receive queue) is returned. If no data is available,
net_error is set to EWOULDBLK and -1 is returned; the r_upcall mechanism
may be used to determine when data arrives. (Technical note:
"r_upcall" is called whenever a PUSH or FIN bit is seen in an incoming
segment, or if the receive window fills. It is called before an
ACK is sent back to the remote TCP, in order to give the user an
opportunity to piggyback any data in response.)
When the remote TCP closes its half of the connection and all prior
incoming data has been read by the local user, subsequent calls to
recv_tcp return 0 rather than -1 as an "end of transmission" indicator.
Note that the local application is notified of a remote close
(i.e., end-of-file) by a state- change upcall with the new state being
CLOSE_WAIT; if the local application has closed first, a remote
close is indicated by a state-change upcall to either CLOSING or
TIME_WAIT state. (CLOSING state is used only when the two ends close
simultaneously and their FINs cross in the mail).
/* Close a TCP connection */
close_tcp(tcb)
struct tcb *tcb;
This tells TCP that the local user has no more data to send. How-
ever, the remote TCP may continue to send data indefinitely to the
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local user, until the remote user also does a close_tcp. An attempt to
send data after a close_tcp is an error.
/* Delete a TCP connection */
del_tcp(tcb)
struct tcb *tcb;
When the connection has been closed in both connections and all incoming
data has been read, this call is made to cause TCP to reclaim the space
taken up by the TCP control block. Any incoming data remaining unread is
lost.
/* Dump a TCP connection state */
state_tcp(tcb)
struct tcb *tcb;
This debugging call prints an ASCII-format dump of the TCP connection
state on the terminal. You need a copy of the TCP specification (ARPA
RFC 793 or MIL- STD-1778) to interpret most of the numbers.
8.6.9. The User Datagram Protocol (UDP)
UDP is available for simple applications not needing the services of a
reli- able protocol like TCP. A minimum of overhead is placed on top
of the "raw" IP datagram service, consisting only of port numbers and a
checksum covering the UDP header and user data. Four functions are
available to the UDP user.
/* Create a UDP control block for lsocket, so that we can queue
* incoming datagrams.
*/
int
open_udp(lsocket,r_upcall)
struct socket *lsocket;
void (*r_upcall)();
open_udp creates a queue to accept incoming datagrams (regardless of
source) addressed to "lsocket". "r_upcall" is an optional upcall
mechanism to provide the address of a function to be called as follows
whenever a datagram arrives:
(*r_upcall)(lsocket,rcvcnt);
struct socket *lsocket; /* Pointer to local socket */
int rcvcnt; /* Count of datagrams pending on queue
*/
/* Send a UDP datagram */
int
send_udp(lsocket,fsocket,tos,ttl,bp,length,id,df)
struct socket *lsocket; /* Source socket */
struct socket *fsocket; /* Destination socket */
char tos; /* Type-of-service for IP */
char ttl; /* Time-to-live for IP */
struct mbuf *bp; /* Data field, if any */
- 104 -
int16 length; /* Length of data field */
int16 id; /* Optional ID field for IP */
char df; /* Don't Fragment flag for IP */
The parameters passed to send_udp are simply stuffed in the UDP
and IP headers, and the datagram is sent on its way.
/* Accept a waiting datagram, if available. Returns length of datagram
*/
int
recv_udp(lsocket,fsocket,bp)
struct socket *lsocket; /* Local socket to receive on */
struct socket *fsocket; /* Place to stash incoming socket */
struct mbuf **bp; /* Place to stash data packet */
The "lsocket" pointer indicates the socket the user wishes to
receive a datagram on (a queue must have been created previously with
the open_udp rou- tine). "fsocket" is taken as the address of a socket
structure to be overwrit- ten with the foreign socket associated
with the datagram being read; bp is overwritten with a pointer to the
data portion (if any) of the datagram being received.
/* Delete a UDP control block */
int
del_udp(lsocket)
struct socket *lsocket;
This function destroys any unread datagrams on a queue, and reclaims the
space taken by the queue descriptor.
CONTENTS
Section Title Page
1. Introduction to TCP/IP and the KA9Q Software 3
1.1. An Overview of the TCP/IP Protocol Family 3
1.1.1. Acknowledgement 3
1.1.2. Introduction 3
1.1.3. What is TCP/IP? 3
1.1.4. General description of the TCP/IP protocols 8
1.1.5. The IP level 12
1.1.6. The Ethernet level 13
1.1.7. Well-known sockets and the applications layer 15
1.1.8. An example application: SMTP 17
1.2. Protocols other than TCP: UDP and ICMP 20
1.3. Keeping track of names and information: the domain system 21
1.4. Routing 22
1.5. Details about Internet addresses: subnets and broadcasting 24
1.6. Datagram fragmentation and reassembly 26
1.7. Ethernet encapsulation: ARP 26
1.8. Getting more information 27
1.9. Overview of the KA9Q Internet Package 29
2. Installation 31
2.1. What an IP Address Is, and How to Get One 31
2.2. Configuring a TNC for TCP/IP Operation 31
2.2.1. TAPR TNC-1 and Clones 31
2.2.2. TAPR TNC-2 and Clones 32
2.2.3. AEA PK-232 32
2.2.4. Kantronics TNC's 33
2.2.5. Paccomm PC-100 Card 34
2.2.6. DRSI 34
2.3. IBM PC and Clones 34
2.3.1. Installing the Plug'N'Play Disk 34
2.3.1.1. The AUTOEXEC.NET File 34
2.3.1.2. The FTPUSERS File 35
2.3.1.3. The HOSTS.NET File 36
2.3.2. Installing on a Hard Disk 37
2.4. Unix 37
2.5. Macintosh 38
2.6. Atari ST 38
2.7. NEC PC-9801 38
2.8. Hewlett-Packard Portable Plus 38
3. Taking NET for a Test Drive 39
3.1. Trying out the AX.25 Support 39
3.2. The Telnet Command 39
3.3. The FTP Command 40
3.4. The Mail System 40
3.5. Tracing and Status Commands 40
4. The Mail System 42
4.1. Installing and Using BM 42
4.1.1. Installation 42
4.1.1.1. Directory Structure 42
4.1.1.2. Configuration File 42
4.1.1.2.1. smtp <path> 43
4.1.1.2.2. host <your hostname> 43
4.1.1.2.3. user <username> 43
4.1.1.2.4. edit <path of your editor> 43
4.1.1.2.5. fullname <your full name> 43
4.1.1.2.6. reply <return address> 43
4.1.1.2.7. maxlet <number of messages> 43
4.1.1.2.8. mbox <filename> 43
4.1.1.2.9. record <filename> 44
4.1.1.2.10. folder <directory name> 44
4.1.1.2.11. screen [bios|direct] 44
4.1.1.2.12. Example BM.RC File 44
4.1.1.3. The alias File 44
4.1.1.4. /spool/mqueue/sequence.seq 45
4.1.2. Environment 45
4.2. Commands 45
4.2.1. Main Menu Commands 45
4.2.1.1. m [userlist] 45
4.2.1.2. d [msglist] 45
4.2.1.3. h 45
4.2.1.4. u [msglist] 46
4.2.1.5. n [mailbox] 46
4.2.1.6. ! cmd 46
4.2.1.7. ? 46
4.2.1.8. s [msglist] [file] 46
4.2.1.9. p [msglist] 46
4.2.1.10. w [msglist] file 46
4.2.1.11. f [msg] 46
4.2.1.12. b [msg] 46
4.2.1.13. r [msg] 47
4.2.1.14. msg# 47
4.2.1.15. l 47
4.2.1.16. k [msglist] 47
4.2.1.17. $ 47
4.2.1.18. x 47
4.2.1.19. q 47
4.2.2. Text Input Commands 47
4.2.3. Command Line Options 48
4.3. Technical Information 48
4.3.1. Outbound Mail Queue File Formats 48
4.3.2. Standards Documents 48
4.4. Bug Reports 49
5. NET/ROM Support 50
5.1. Introduction 50
5.2. Setting up the NET/ROM Interface 50
5.3. Tracing on the NET/ROM Interface 50
5.4. Routing Broadcasts 50
5.5. The NET/ROM Routing Table 51
5.6. The Importance of the Routing Table 52
5.7. Interfacing with NET/ROMs Using Your Serial Port 53
5.8. The Time to Live Initializer 53
5.9. Using NET/ROM Support for IP 53
5.10. The NET/ROM Transport Layer 54
5.11. Connecting via NET/ROM Transport 55
5.12. Displaying the Status of NET/ROM Connections 55
5.13. NET/ROM Transport Parameters 55
5.14. The Mailbox 56
5.15. Where to go for More Information 56
5.16. About the Code 56
6. Advanced Topics 58
6.1. The Finger Server 58
6.2. The GRAPES Multi-Port Digipeating Code 58
6.3. Multiple Serial Ports on One Interrupt 59
7. NET Command Reference 60
7.1. Startup 60
7.2. Console Mode 60
7.3. Commands 60
7.3.1. <cr> 61
7.3.2. ! 61
7.3.3. # 61
7.3.4. arp 61
7.3.4.1. arp add <hostid> ether|ax25|netrom <ether addr|callsign> 61
7.3.4.2. arp drop <hostid> ether|ax25|netrom 61
7.3.4.3. arp publish 61
7.3.5. attach 61
7.3.5.1. HP Portable Specifics 63
7.3.5.2. SLIP Modem Dialing 63
7.3.6. ax25 64
7.3.6.1. ax25 digipeat [on|off] 64
7.3.6.2. ax25 heard [on|off] 64
7.3.6.3. ax25 maxframe [<val]>] 64
7.3.6.4. ax25 mycall [<call>] 64
7.3.6.5. ax25 bbscall [<call>] 64
7.3.6.6. ax25 paclen [<val>] 64
7.3.6.7. ax25 pthresh [<val>] 65
7.3.6.8. ax25 reset <axcb> 65
7.3.6.9. ax25 retry [<val>] 65
7.3.6.10. ax25 status [<axcb>] 65
7.3.6.11. ax25 t1|t2|t3 [<val>] 65
7.3.6.12. ax25 window [<val>] 65
7.3.7. close [<session #>] 65
7.3.8. connect <interface> <callsign> [<digipeater> ... ] 65
7.3.9. dir [<dirname>] 66
7.3.10. disconnect [<session #>] 66
7.3.11. echo [accept|refuse] 66
7.3.12. eol [unix|standard] 66
7.3.13. escape <char> 67
7.3.14. etherstat 67
7.3.15. exit 67
7.3.16. finger 67
7.3.17. ftp <hostid> 67
7.3.17.1. abort 67
7.3.17.2. dir [<file>|<directory> [<localfile>]] 67
7.3.17.3. get <remote_file> [<local_file>] 68
7.3.17.4. ls [<file>|<directory> [<localfile>]] 68
7.3.17.5. mkdir <remote_directory> 68
7.3.17.6. put <local_file> [<remote_file>] 68
7.3.17.7. rmdir <remote_directory> 68
7.3.17.8. type [a|i|l<bytesize>] 68
7.3.18. help 69
7.3.19. hostname [<name>] 69
7.3.20. log [stop|<file>] 69
7.3.21. ip 69
7.3.21.1. ip address [<hostid>] 69
7.3.21.2. ip status 69
7.3.21.3. ip ttl [<val>] 69
7.3.22. memstat 69
7.3.23. mode <interface> [vc|datagram] 69
7.3.24. mulport [on|off] 70
7.3.25. param <interface> [param] 71
7.3.26. pwd [<dirname>] 71
7.3.27. record [<filename>|off] 71
7.3.28. reset [<session>] 71
7.3.29. route 71
7.3.30. session [<session #>] 72
7.3.31. shell 73
7.3.32. smtp 73
7.3.32.1. smtp gateway [<hostid>] 73
7.3.32.2. smtp kick 73
7.3.32.3. smtp maxclients [<val>] 73
7.3.32.4. smtp timer [<val>] 73
7.3.32.5. smtp trace [<val>] 73
7.3.33. start 73
7.3.34. stop 74
7.3.35. tcp 74
7.3.35.1. tcp irtt [<val>] 74
7.3.35.2. tcp kick <tcp_addr> 74
7.3.35.3. tcp mss [<size>] 74
7.3.35.4. tcp reset <tcb_addr> 74
7.3.35.5. tcp rtt <tcp_addr> <rtval> 74
7.3.35.6. tcp status [<tcb_addr>] 74
7.3.35.7. tcp window [<val>] 75
7.3.36. telnet <hostid> 75
7.3.37. trace [<interface> [<flags>]|allmode|cmdmode] 75
7.3.38. udp status 75
7.3.39. upload [<filename>] 75
7.3.40. ? 75
8. Appendices 76
8.1. Obtaining Current Bits 76
8.1.1. Via FTP on the Internet 76
8.1.2. On PC Floppies 76
8.1.2.1. WB3FFV's Phone BBS in the USA 76
8.1.2.2. PA0GRI's Phone BBS in Holland 77
8.1.3. Gary Sanders' Phone BBS in the USA 77
8.1.4. Michael Broqvist in Sweden 77
8.2. The KISS Specification 78
8.3. The KISS Host to TNC Protocol 78
8.3.1. The Protocol Specification 78
8.3.1.1. Introduction 78
8.3.1.2. Asynchtronous Frame Format 78
8.3.1.2.1. Transparency 79
8.3.1.3. Control of the Raw TNC 79
8.3.1.4. Persistence 80
8.3.2. The TNC-2 Implementation 80
8.3.3. The TNC-1 Implementation 81
8.3.4. The VADCG/ASHBY Implementation 81
8.3.5. The AEA Implemenation 81
8.3.6. The Kantronics Implemenation 81
8.4. The FTP, Inc., Packet Driver Specification 81
8.4.1. Introduction and Motivation 81
8.4.2. Identifying network interfaces 82
8.4.3. Initiating driver operations 83
8.4.4. Programming interface 83
8.4.4.1. Entry Conditions 84
8.4.4.2. Byte ordering 84
8.4.4.3. driver_info() 84
8.4.4.4. access_type() 85
8.4.4.5. release_type() 86
8.4.4.6. send_pkt() 86
8.4.4.7. terminate() 87
8.4.4.8. get_address() 87
8.4.4.9. reset_interface() 87
8.4.4.10. set_rcv_mode() 88
8.4.4.11. get_rcv_mode() 89
8.4.4.12. set_multicast_list() 89
8.4.4.13. get_multicast_list() 89
8.4.4.14. get_statistics() 90
8.4.4.15. set_address() 90
8.4.5. Interface classes and types 91
8.4.6. Function call numbers 92
8.4.7. Error codes 92
8.4.8. 802.3 vs. Blue Book Ethernet 93
8.5. Information for Software Developers 93
8.6. Technical Information for Client/Server Developers 94
8.6.1. Data Structures 94
8.6.2. Timer Services 95
8.6.3. Internet Type-of-Service 95
8.6.4. The Internet Protocol Implementation. 95
8.6.5. IP Gateway (Packet Router) Support 95
8.6.6. IP Interfaces 96
8.6.7. IP Host Support 98
8.6.8. The Transmission Control Protocol (TCP) 99
8.6.9. The User Datagram Protocol (UDP) 103
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