466 lines
24 KiB
Plaintext
466 lines
24 KiB
Plaintext
Obtaining Host and Address Information
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Ron Ray
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Network Services Group
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Homewood Academic Computing
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Johns Hopkins University
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(draft manuscript)
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Electronic mail is one of the most popular facilities used on wide area
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networks. Users separated by hundreds or thousands of miles can exchange
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messages and documents on-line, usually in a small period of time. Like
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U.S. postal mail, electronic mail uses an addressing scheme to ensure
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correct delivery of messages. Unlike U.S. postal mail, the form of the
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electronic mail address varies from one network to the next. In general,
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an electronic mail address is composed of a username and a computer host
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name. Unfortunately, there is no general scheme for disseminating host
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names and usernames.
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Finding information about a host on a wide-area network can be
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surprisingly difficult. One common problem involves finding information
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about a username and a host name when only a personal name and an
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organization name is available. The best solution to this problem is to
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contact the person by mail or phone and ask for their username and
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network address. Unfortunately, this is not always possible. The user
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may not be available or they may not know their network address. Other
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common problems include finding a network address when only the host
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name is known and finding a username when the network address is known
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but the username is not known. If there is no way to contact the
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intended recipient by mail or phone, a detective game must be played
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using whatever resources a given network provides. These resources vary
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from network to network. They are often indifferently documented and
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sometimes several overlapping resources are available on the same
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network. The purpose of this document is to acquaint the reader with
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some of the resources that are available and how they are used.
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I. Bitnet. The Bitnet is a wide-area network of about 3000 hosts
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connected mostly by point-to-point links. Address information is
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probably easier to come by on the Bitnet than other wide area networks.
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This is due to several factors, One, all Bitnet host names are included
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in a single file that's kept on every host connected to the Bitnet. An
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organization name is usually included following the Bitnet address. It's
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possible to search this hosts file using the organization name as the
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search string, and find the host address or addresses associated with
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this organization. The name and location of this file should be obtained
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from the system administrator since it varies from system to system.
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Second, there is a central facility which provides a database,
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informational files and other resources about Bitnet. Finally, there are
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a variety of other hosts, called listservs, that provide files,
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databases of usernames and other resources.
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The Bitnet Information Center keeps files of host names, host
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information, gateways to other networks, etc. on line for retrieval. In
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addition, some files can be searched with a database server which will
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return, via mail, only those records that are selected by the search.
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The host name associated with the Bitnet information center is Bitnic.
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I.1. Netserv. A list of files available from Bitnic can be retrieved by
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sending the following interactive command to Bitnic's file server
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(named netserv):
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$ send netserv@Bitnic get netserv filelist ! for VMS machines running JNET
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tell netserv at Bitnic get netserv filelist ! for VM/CMS machines
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Note, most of these files are lists of other files that can be received.
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A particular file can be retrieved with the command:
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$ send netserv@Bitnic get <filename> <filetype> ! for VMS machines
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tell netserv at Bitnic get <filename> <filetype> ! for VM/CMS machines
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One important piece of information that can be retrieved in this fashion
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is the so-called node entry. This record contains things like the
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electronic mail address of the host administrator, the type of computer
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etc. Sometimes the Bitnet host name is known but the mail recipient's
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username is not known. In this case, the host node entry can be
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consulted for the postmaster's electronic mail address. The postmaster
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can be asked, via mail, for information about the desired address.
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The node entry information can be obtained with the following command:
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$ send netserv@Bitnic get nodentry <nodename> ! for VMS machines running
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JNET
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tell netserv at Bitnic get nodentry <nodename> ! for VM/CMS machines
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More information about using netserv at Bitnic can be obtained with the
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command:
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$ send netserv@Bitnic get helpfile ! for VMS machines running
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JNET
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tell netserv at Bitnic get helpfile ! for VM?/CMS machines
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It's also worth noting that netserv commands can be placed in the first
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line of a mail message sent to netserv@Bitnic.
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I.2. Database. Bitnic also provides a database server that allows
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selective access to its database files. One useful thing that can be
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done with database is to find all the Bitnet sites in a particular
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state. For example, the command:
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$ Send database@Bitnic FIND STATE DC (FORMAT NAMESFRM
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tell netserv at Bitnic FIND STATE DC (FORMAT NAMESFRM
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returns a list of all Bitnet hosts in Washington DC. Individual host
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information can be retrieved by sending the command:
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$ Send database@Bitnic FIND HOST <hostname>
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tell database at Bitnic FIND HOST <hostname>
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Database can also be used to search mailing list archives. More will be
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said about this later.
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Internet hosts without direct Bitnet access can send send mail commands
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to database@Bitnic. To do this they must register with the database
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server and receive a password. This procedure, as well as general
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database help, is provided by sending mail to database@Bitnic with the
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command "help" in the first line of text.
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I.3. Listservs. Listserv is software developed for IBM Bitnet hosts. The
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original function of this software was to service mailing lists. Since
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then the software has been updated to offer other features such as file
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service, user directory service , on-line help and a database server. A
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list of listserv servers (and other Bitnet servers) can be obtained by
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sending the command:
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$ send service@Bitnic get Bitnet servers
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tell service at Bitnic get Bitnet servers
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One of the things that is contained in this file is a list of listsrv's
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that have user directory services. If it's necessary to find someone's
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username at one of these hosts, the command:
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$ send listserv@<nodename> /whois <search-string>
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tell listserv at <nodename> /whois <search-string>
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where search-string is a personal name or some substring of a personal
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name, will return the username associated with the search string (if its
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in their database). Some listserv's maintain a general user directory
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service for users anywhere on the Bitnet. Unfortunately, there is no
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simple way to find out who subscribes to these listservs. The listserv
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at the host marist has the largest collection of usernames since it
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keeps the names of anyone who who ever subscribed to a Bitnet mailing
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list.
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A list of Bitnet related files can be obtained from listserv by means of the
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command:
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$ send listserv@Bitnic get netinfo filelist
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tell listserv at Bitnic get netinfo filelist
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Listservs also have a database server. Documentation for the database
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server is contained in the file listdb memo.
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II. The Internet. The Internet is a rapidly growing wide-area network of
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more than 100,000 hosts. It is not really a single network. Instead, it
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is a network of networks, partitioned in a tree-like fashion. The
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partitions, and sub-partitions, etc. are called domains. Responsibility
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for the internet domains is largely local to the domain. Each domain has
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its own organization and contacts. Information about hosts associated
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with a domain are provided by the domain name service. Several hosts
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associated with a given domain are designated as nameservers for the
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domain. The nameservers keep information about the other hosts
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associated with the domain and /or other nameservers associated with
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further partitions of their domain. Internet hosts needing address
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information about hosts associated with a domain automatically query
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the appropriate nameserver. Note, internet hosts running old versions
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of the internet communications software, tcp/ip, may be unable to do
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this. These hosts have to resort to using large but incomplete tables
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of internet hosts. Overall responsibility for the internet is
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associated with the Network Information Center, NIC. NIC provides
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information about first and second level domains, manages the
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registration of domains and provides general support for the internet.
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Troubles with host names and addresses and with E-mail addresses can
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often be resolved by first using facilities provided by nic, such as
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whois, and then manually querying the Domain Name Service for local
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domain information.
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II.1. The whois database maintains information about hosts, domains and
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users. Information from the database can be obtained by running a whois
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client program from a remote host, by telneting to nic.ddn.mil and
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running the whois program interactively, or by sending mail to
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server@nic.ddn.mil with a database query in the subject line. Note,
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telnet is the remote login application provided with tcp/ip.
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Not all hosts on the internet are in the whois database. Instead,
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information about the top two domains is maintained. This information
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includes an E-mail address of a contact person for that domain. Some
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individual hosts and individual usernames are also registered with the
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NIC and therefore available from whois.
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Information about domains can be obtained by issuing the following
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command:
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whois domain jhu.edu ! where jhu.edu is the domain for
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! which information is desired
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This command can be included in the subject line of a mail message sent
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to service@nic.ddn.mil. Information returned by this query includes the
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E-mail address of the responsible person for the domain, organization
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name and address and addresses of the domain name servers.
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A wildcard search can be done by including a dot or dots after the
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argument. This will match all records whose specified field begins with
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the argument. Note, a general search on all fields of the database can
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be achieved by leaving off the keyword argument and simply typing in the
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text to be searched for. For example, the following query would return
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several records, one of which would be the domain jhu.edu:
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whois jhu...
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If a general search is done and/or if a wildcard is used many database
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entries may be located. In this case a summary of the records found will
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be returned. Full information on a particular record can then be
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requested by specifying the desired record more completely as, for
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example, "domain jhu.edu", or by specifying the record's handle in the
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database query. A record's handle is a unique identifier associated with
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each record in the database. The handle is always enclosed in
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parentheses and always follows the record's name. A query of the form:
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whois handle net-jhu
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will return just the record associated with the handle net-jhu. Some
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record types have subdisplays associated with them. A subdisplay is
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simply additional information associated with a record. For example,
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host records have a subdisplay of registered users. The output keyword
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of "expand" forces the output of all subdisplays associated with a
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record. The following query will show all the registered users
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associated with the host jhunix.hcf.jhu.edu:
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whois host expand jhunix.hcf.jhu.edu
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If some information is known about an internet hosts domain,
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organization name, or other associated field, whois can be used to
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initiate a hierarchical search for the necessary information. Locating
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the domain or network record will provide a E-mail address. Inquiries
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could be made to this address for other E-mail addresses associated
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with lower level domains or individual hosts that might be able to
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provide help. Alternately, the domain service addresses provided could
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be used with another utility called nslookup to obtain further
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information. Finally, the desired host or E-mail address information may
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be directly obtainable from whois. The proportion of registered to
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non-registered hosts and addresses is small, however. The query:
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whois help
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can be used to obtain more information about the use of whois. It should
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be noted that some client versions of whois have a different command
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syntax then that described above.
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II.2. A number of online files are kept at NIC. These include files
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containing addresses of responsible persons for domains, files
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detailing host administrator duties, etc. They can be accessed by
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anonymous FTP or by sending mail to service@nic.ddn.mil. To get a list
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of what types of files are available, send mail to service@nic.ddn.mil
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with the command "help" in the subject line: To retrieve a specific
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file, use the command "send XXX" where XXX is a fully specified
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filename. For example, host administrator addresses are contained in the
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file named hadminbyaddr.txt located in the netinfo directory. The
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command:
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send netinfo:hadminbyaddr.txt
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when included in the subject line of a mail message to
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service@nic.ddn.mil can be used to obtain the file by mail.
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II.3 Nslookup. Nslookup is a utility that allows users to query
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nameservers. It can be used to get addresses associated with host
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names, host names associated with addresses, mail addresses of the
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server manager, as well as to locate a server associated with a
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particular domain.
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Some tcp/ip implementations don't have the ability to use nameservers.
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Instead, they keep tables of addresses and host names. If these hosts
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need to access another host whose address is not in their table, they
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can consult someone with access to nslookup to obtain the address.
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Addresses associated with a particular domain name can be obtained by
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typing the domain name in response to the nslookup prompt. For example,
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the address associated with the host name jhmail.hcf.jhu.edu would be
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obtained as follows:
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$ nslookup > jhmail.hcf.jhu.edu
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Sometimes users will have a particular address and will want to know the
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host name associated with the address. To obtain a host name
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associated with a particular address the address is entered with the
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bytes reversed followed by .in-addr.arpa. For example, to get the host
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name associated with the address 128.220.2.7 type:
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$ nslookup
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nslookup> set query=ptr
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nslookup> 7.2.220.128.in-addr.arpa
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The nameservers allow hosts that are not really internet hosts to appear
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to be on the internet. This is done by means of mail exchange or MX
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records. Unfortunately, not all mailers can do MX lookups. When the
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situation occurs where a correct appearing address doesn't work with
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mail or where a simple nslookup query for the address doesn't work, the
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nameserver should be queried for the existence of an MX record. This can
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be done by entering:
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nslookup> set query=mx
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nslookup> enter-the-address-here
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If an MX record exists for an address and if a particular mailer can't
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do MX lookups, an address of the following form will probably work:
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username%mail-address@MX-address
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Nslookup can be used to provide information about who maintains a
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domain's nameserver. This user, the hostmaster, may be able to provide
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additional information when contacted via E-mail. If a nameserver
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associated with a particular domain is known, the procedure is as
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follows:
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nslookup>server enter-the-server-name-here
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nslookup> set debug
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nslookup> enter-hostname-here
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A variety of debugging information will be returned, one item of which
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is the E-mail address of the hostmaster. The relevant line of output
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will begin with the string "mail addr =" . The mail address is in the
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form:
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username.hostname.domain-name
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and will have to be changed to:
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username@hostname.domain-name
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In the above situation, the address of the nameserver associated with a
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given domain is often not known. A local nameserver can be used to
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provide this information in the debug mode by giving it a dummy address
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consisting of a "made-up"hostname followed by a correct domain portion
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of the address. For example, if information about the umd.edu domain
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nameservers is needed, nslookup would be placed in debug mode and given
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the address anything.umd.edu. The query will probably fail but the
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debugging information returned will include the namesever addresses
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associated with the domain.
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A listing of hosts by domain can be obtained from nslookup by using the
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"ls <domain>" command where domain is the domain associated with the
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nameserver.
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Bitnet users with no direct access to nslookup can still get the basic
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nslookup information by sending mail to nslookup@sh.cs.net. Domain style
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addresses can be placed in the body of the message, one per line, and
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mail will be returned listing all the nameserver records for the named
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domains.
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III.UUCP. The uucp software developed for Unix systems has been used to
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create a wide-area network. This network is even less centralized than
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the internet. Access to this network is gained by running uucp and
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getting dial-up access to another host already on the network. There are
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no official requirements for membership and hosts can join or leave the
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network in an unobtrusive fashion. This informality frequently produces
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problems with addressing. The Uucp project was created to deal with
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these problems. "Official" uucp hosts register their name with the Uucp
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project at host uunet. Maps of the uucp network are available from uunet
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and can be used by software named Pathalias to route information between
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uucp hosts. Formerly, users had to specify the entire route in a so
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called "bang style" address. A "bang style" address looks like
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hosta!hostb!hostc!username. A mail message sent with this address would
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travel to hosta, then to hostb and finally to hostc.
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Users connected to the uucp network rarely have to specify routing
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information in the E-mail address. Pathalias usually handles the
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routing. Occasionally, however, some problem will arise where some
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routing information must be obtained, such as fixing a garbled return
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address. In addition, since uucp hosts can have a domain style name,
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it is sometimes neccessary to determine whether a host is really a
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uucp host, or whether it's an internet host.
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Interactive information about a UUCP host can be obtained by sending an
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interactive Bitnet command of the following form:
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$ send/command psuvax1 uuhosts <uucp-host-name>
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SM RSCS CMD PSUVAX1 uuhosts <uucp-host-name>
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Information about the path to the host can similarly be obtained by:
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$ send/command psuvax1 uupath <uucp-host-name>
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SM RSCS CMD PSUVAX1 uupath <uucp-host-name>
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The UUCP maps can be examined to get items like the postmaster address,
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mailing address, etc. The maps are posted in the USENET group
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comp.mail.maps and must be unpacked or uncompressed. These maps are also
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available for anonymous FTP from uunet.uu.net in directory uumap.
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IV. Info-nets. Info-nets is a mailing list that provides information
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about addresses, location of users and gateways, and similar matters.
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Questions can be sent to the list and experienced members of the list
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will attempt to provide answers. The list can be subscribed to by
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sending a subscription request to info-nets-requests@think.com.
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Questions are addressed to info-nets@think.com. Questions that include
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as much information as possible, such as full headers of bounced mail
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messages, etc. are most likely to be answered. Archives of info-nets
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questions and answers are kept on some Bitnet servers, such as the one
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at Bitnic. Users can request these files using the interactive netserv
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or listserv commands outlined in the beginning of this document. A list
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of the archives can be obtained with the interactive command:
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$ send listserv@Bitnic get notebook filelist
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tell listserv at bitnic get notebook filelist
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This returns a list of all the archive files stored on Bitnic. Each
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archive or notebook is named infonets logXXXX where XXXX is a date like
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8909. For example, the infonets archive for September 1989 can be
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obtained with the interactive command:
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$ send listserv@Bitnic get infonets log8909
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tell listserv at Bitnic get infonets log8909
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In addition, the archives can be searched using the database server at
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Bitnic. A text search for the string china would be formatted as
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follows:
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$ send database@Bitnic find text China (in infonets
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tell listserv at Bitnic find text China (in infonets
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Remember, internet hosts without direct Bitnet access can send mail
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commands to database. To do this they must register with database and
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receive a password. This procedure, as well as general database help, is
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provided by sending mail to database@Bitnic with the command
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"help" in the first line of text. The listserv database server, Ldbase,
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can be also be accessed via E-mail (see section I.3.) and used to search
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infonets archives.
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V. Further information. Several books have recently been published which
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provide information about networks, gateways, addresses and network
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resources. They are listed below.
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The Matrix: Computer Networks and Conferencing Systems Worldwide
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by John S. Quarterman, Digital Press, 1989.
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Users' Directory of Computer Networks
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by Tracy Lynn LaQuey, Digital Press, 1989.
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A Guide to Electronic Mail Networks and Addressing
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by Donnalyn Frey and Rick Adams, O'Reilly & Associates, 1989.
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