[3845] in linux-net channel archive
Re: 2.0.x TCP problem?
daemon@ATHENA.MIT.EDU (Eric Schenk)
Thu Jul 25 05:24:51 1996
To: Marek Michalkiewicz <marekm@i17linuxb.ists.pwr.wroc.pl>
cc: linux-net@vger.rutgers.edu
In-reply-to: Your message of "Tue, 23 Jul 1996 14:46:13 EDT."
<199607231846.UAA00620@i17linuxb.ists.pwr.wroc.pl>
Date: Wed, 24 Jul 1996 12:21:05 -0400
From: "Eric Schenk" <schenk@cs.toronto.edu>
Marek Michalkiewicz <marekm@i17linuxb.ists.pwr.wroc.pl> writes:
>I just noticed something which I think could be a problem with
>TCP in either 2.0.x or 1.2.13. When I telnet from a machine
>running 2.0.8 (same problem with 2.0.0) to a machine running
>1.2.13, everything is fine until I try to cat a large file.
>At this point the telnet session freezes for about a minute.
>The problem is reproducible every time I try it. It happens
>with telnet, but not with ssh (which works just fine) and not
>when transferring large files using ftp.
Hmm. looking at the log files it looks like a problem with fragmentation.
Possibly the MTU settings are misconfigured somewhere on your network?
(It's a bit difficult to say what is going on because I can't see the
start of the TCP session in this dump.)
>20:23:05.666111 A.1038 > B.telnet: P 2681480523:2681480525(2) ack 484051729 win 15360 (DF)
>20:23:05.666111 B.telnet > A.1038: . ack 2 win 14333
>20:23:05.666111 B.telnet > A.1038: P 1:3(2) ack 2 win 14335
>20:23:05.686112 A.1038 > B.telnet: . ack 3 win 15360
>20:23:05.756112 B.telnet > A.1038: P 3:983(980) ack 2 win 14335 (frag 10234:1000@0+)
Ok, we get the first fragment of a fragmented packet, going from 3:983,
>20:23:05.796113 B.telnet > A.1038: P 1026:2006(980) ack 2 win 14335 (frag 10235:1000@0+)
Next packet sent goes from 1025:2006, what happened to 983:1026?
Eventually something goes right and we get:
>20:23:56.986761 B.telnet > A.1038: P 3:1026(1023) ack 2 win 14335
>20:23:57.006761 A.1038 > B.telnet: . ack 9642 win 11264
>20:23:57.006761 B.telnet > A.1038: P 9642:10063(421) ack 2 win 14335
>20:23:57.026762 A.1038 > B.telnet: . ack 10063 win 12288
and things continue. In any case, what ever is going on, it doesn't
look like a TCP problem to me.
-- eric
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Eric Schenk www: http://www.cs.toronto.edu/~schenk
Department of Computer Science email: schenk@cs.toronto.edu
University of Toronto
