168 lines
6.9 KiB
Plaintext
168 lines
6.9 KiB
Plaintext
Using remote host computers via Telnet
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Understanding Telnet
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The one common element across the disparate environments of the
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Internet is the TCP/IP software protocol suite, the basis of
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communications.
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Telnet, the terminal-handler portion of the TCP/IP protocol suite,
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is the cornerstone of this striking communications technology.
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Telnet handles the remote login to another Internet host, so it is
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useful to know something about the way it works.
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Telnet operates in a client/server environment in which one host
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(the computer you are using, running Client (User) Telnet)
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negotiates opening a session on another computer (the remote host,
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running Server Telnet). During the behind-the-scenes negotiation
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process, the two computers agree on the parameters governing the
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session. One of the first things they settle is the terminal type
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to be used -- in general, a line-by-line network virtual terminal,
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for simplicity's sake. Virtual terminal, in this context, refers to
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a set of terminal characteristics and sequences that both sides of a
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network connection agree to use to transmit data from terminals
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across the network, regardless of the terminal used.
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Finding Telnet Commands
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Try typing "help" or "?" at the Telnet prompt to get a list of
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the commands available in your Telnet software.
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Using Local versus Remote Commands
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Once you have established a remote session, all commands you
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type will be sent to the Server Telnet on the remote host for
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execution.
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If you want a Telnet command issued in the remote environment to
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be acted on locally by your client Telnet, on most systems you
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would normally precede the command with an escape sequence (a
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predetermined character or combination of characters that
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signal your Telnet software to execute the command that follows
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locally). For example, in NCSA Telnet for pc-compatible
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microcomputers, the F10 key is the escape character that alerts
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Telnet to execute locally the next command you type (to turn
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local echo on or off, or to toggle capture on or off, etc.).
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The Telnet escape sequence by itself followed by <cr> returns you
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temporarily to your local operating environment. On UNIX systems,
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the escape sequence is usually the control key (CNTL) and left bracket
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([) pressed simultaneously.
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Logging On
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TELNET <host>
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or
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TELNET <cr> followed by OPEN <host> at the prompt.
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The basic command set is simple. You also need to know either the
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machine domain name or the machine Internet address (a series of
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numbers). The numbers will always work; the names will work if
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they are in a software table available to your version of Telnet.
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IBM systems that use TN3270 may require you to type a carriage
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return, "DIAL VTAM," or just "VTAM" in response to the first
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prompt from the remote system.
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Logging Off
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LOGOFF or LOGOUT (also try QUIT, END, EXIT, STOP, etc.)
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CLOSE, prefixed by the escape sequence.
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ABORT, prefixed by the escape sequence--use as a last resort!
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To exit the remote system, first try that system's logoff
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command. To determine what the appropriate logoff command is,
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check the menus, help, and welcome screens when you first log on.
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Oftentimes, the logoff information is listed there but not always
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easy to retrieve later.
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Logging off the remote system may return you to your primary
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operating environment (all the way out of Telnet), or you may
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be left in Telnet. If so, type "quit".
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But some information systems have no graceful exit for remote
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users. In that case, you have two options --- CLOSE or ABORT.
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CLOSE should be your next choice after LOGOFF. If you are
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unable to CLOSE the connection normally (e.g., if your remote
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session is hung), try the Telnet ABORT command to drop your
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connection locally.
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ABORT will return control to you in your local environment, but
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it may not properly terminate your session on the remote machine.
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Since this can leave the port on the remote machine busy for an
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indefinite period even though you are no longer using it, ABORT
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should be used only as a last resort.
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In either case, you can also try escaping back to your local
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environment and then issuing the termination commands. If one
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method doesn't work, try the other.
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Other commands may allow you to control your communications environment.
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Investigate the help systems both in your local Telnet and on the
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remote system at the outset.
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Using the BREAK Key
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Don't be hasty with the Break key. Too many Breaks may cause
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your Telnet session to be dropped!
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There is no standard BREAK key across versions of Telnet and in
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remote information systems. Telnet is based on the concept of a
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network virtual terminal, in which the control functions (breaks,
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etc.) are communicated with characters regardless of terminal type
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(rather than line conditions, used in the terminal server
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environment). Your local Telnet receives your break and sends out
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a character sequence which is reinterpreted on the other end,
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hopefully as the break you intended.
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Your Break may not always be understood by the remote system, so
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you should try HELP or ? when you begin (at the Telnet prompt)
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to determine what your version of Telnet uses as BREAK.
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Tips: In UNIX, CNTL-C may work for BREAK. In the Mac environment,
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BREAK may be a click down menu option or a character combination.
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In NCSA Telnet (a popular PC version), BREAK is F10 followed by a
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lower case letter "b".
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Using the Backspace Key
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The backspace character may not be recognized by the remote
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system. Investigate in your local Telnet how to set an erasing
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backspace. Type ? at the Telnet prompt, or SET ? for a list of
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possibilities.
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Adjusting the Settings to your Needs
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Most Telnet programs have the ability to SET or TOGGLE many of
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these settings on and off. Erasable backspace, local echo,
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carriage return interpretation (<cr> or <cr><lf> -- i.e.,
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carriage return or carriage return with line feed), and the
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escape character you use to return to the local environment are
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things that you can usually SET or TOGGLE at the Telnet prompt.
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Type ? and use Telnet's internal help system to change a setting.
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Using Function Keys
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Remember that special function keys are local implementations
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and have no significance in a remote session. Function keys
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such as INSERT, DELETE, ERASE END-OF-FIELD, PF, and PA keys may
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not be recognized in the remote environment. Even though
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function keys and control key combinations may have significance
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on the remote system, they may vary from those on your local
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system.
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==== <g REMOTE> 2 links in glossary topic
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