Re: Telnet Negotiation Question!
From: Doug Mitton (doug_mitton_at_hotmail.x.com)
Date: 12/10/03
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Date: Wed, 10 Dec 2003 15:07:35 -0500
mru@kth.se (Måns Rullgård) wrote:
>Doug Mitton <doug_mitton@hotmail.x.com> writes:
>
>> I am searching for "readable" telnet negotiation information but I
>> thought I'd ask here in the meantime in case someone has a reference
>> or suggestion handy.
>
>RFC854, http://www.rfc-editor.org/rfc/rfc854.txt, looks pretty
>readable to me.
I had been reading Googled answers to questions, source code snips and
whole source code downloads. I hadn't looked into RFC's before as
(for some reason) I thought they read like MAN pages ... which can be
rather cryptic. Yes, the first one I hit was RFC 0008 and it was
completely readable and told me my problem right near the end of the
document.
>> I guess my basic question is ... is it possible to put a telnet server
>> into RAW (?) mode so that it doesn't watch the transfering stream for
>> re-negotiation requests?
>
>I'll let someone else come with a definitive answer, but I doubt it.
>I can't remember ever reading about anything like that.
There is a BINARY mode BUT it still allows the xFF monitoring and it
must still be escaped.
>> I am having a problem in my application and it looks like a byte is
>> showing up in the data stream that the originator didn't send. I am
>> assuming that the telnet server is adding it as it looks very similar
>> to a negotiation request.
>>
>> The bytes in question (in the packet header) look like:
>>
>> sent by originator: x01 xFF x00
>> receiver gets: x01 xFF xFF x00
>
>A 0xff character means that the next character is a telnet command.
>To send a literal 0xff, it needs to be escaped with an extra 0xff.
>Thus, if the telnet server or client receives such a character as
>user/application input, it will add the escaping.
>
>> I'm not 100% certain telnetd is the culprit but I'm looking for
>
>I'd say that's the case. Is your program acting as either telnet
>server or client? Otherwise you shouldn't need to worry about these
>things.
My program is acting as a client to the Kegs emulator AND a client to
telnetd, I am simply "crossing" the sockets so the 2 can talk to each
other; that is an old Apple // terminal emulator program can now
actually get out on the internet as a telnet client.
I have modified my program to capture xFF bytes and escape/unescape as
required BUT the Xmodem protocol is still claiming a malformed header
when the transfer hits packet 254. So, I'm off to take a look at
Xmodem specs.
Thanks for the response and the link to RFC's!
--
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