Re: TELNET question

Theodore Ts'o <> Wed, 16 November 1994 05:21 UTC

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From: Theodore Ts'o <>
Message-Id: <9411160443.AA23214@dcl.MIT.EDU>
To: William Chops Westfield <>
In-Reply-To: William "Chops" Westfield's message of Tue, 15 Nov 94 17:46:59 PST, <>
Subject: Re: TELNET question
Address: 1 Amherst St., Cambridge, MA 02139
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   Date: Tue, 15 Nov 94 17:46:59 PST
   From: William "Chops" Westfield <>

   Well, this makes the tester pretty broken.  A lot of client telnet
   implementations assume that the server is going to initiate
   negotiations for most features.  If the tester doesn't, it won't test
   the most commonly used paths...

   A lot of unix telnets detect when the remote port is NOT the telnet
   port, and start up the connection with a lot of local handling (line
   mode, local interrupts, etc.)  I'm not sure that the initial settings
   would be the same in the abscense of telnet negotiations on the normal
   telnet port or not.

What many telnets do is that if the remote port is NOT the telnet port,
then they will *not* try to initiate any options negotation.  This is
because many users use telnet as a convenient way to talk to other
servers, such as SMTP or NNTP servers, by doing "telnet machine 25" and
type SMTP commands at it.  Since the SMTP deamon isn't a telnet server
at all, it would get really confused by a series of telnet options
negotiation sequences.  (However, the client telnet will accept any
option negotiations that the server offers.)

						- Ted