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SubjectRe: IPv4: ssh failure, local port 1023


On Tue, 1 Dec 1998, Geert Uytterhoeven wrote:

> Date: Tue, 1 Dec 1998 19:20:03 +0100 (CET)
> From: Geert Uytterhoeven <Geert.Uytterhoeven@cs.kuleuven.ac.be>
> To: Linux kernel <linux-kernel@vger.rutgers.edu>
> Subject: IPv4: ssh failure, local port 1023
>
>
> Sometimes I have problems using ssh to log in. The ssh connection just doesn't
> seem to succeed. Using the `-v' option, the last line it prints is
>
> Allocated local port 1023
>
> If I CTRL-C and retry, it fails again (reproducible). However, if I retry
> without breaking the first attempt, ssh gets allocated a different local port
> number and the connection succeeds.
>
> The sshd runs on a Pentium with 2.0.35, ssh client runs on a 68040 with
> 2.1.130.
>
I have also had this problem quite a few times.
I cannot explain exactly how this happens, but the patterns seems to be as
follows:
netstat -a on a destination host (where sshd is run) shows that
there is a connection from client machine with port number, say 1023,
which is not quite finished (on FreeBSD mchine netstat reports it as
having state of TIME_WAIT)
On the client machine netstat -a shows a connection from the same 1023
port in state SYN_SENT;
Unfortunately I cannot find an easy way to produce this on purpose.

> But I've been seeing this on different types of machines, running both
> Linux/m68k and Linux/ia32, with both 2.0.x and 2.1.x kernels, since more than a
> year. There seems to be one common thing in the failures: the allocation of
> the local port 1023. It doesn't always fail if the local port is 1023, but if
> it fails, it's always 1023.
>
This would depend on number of ssh sessions you are running on your
machine? Strange ...

> Needless to say, this is hard to track. Just when I wanted to start using
> tcpdump, I couldn't reproduce the problem anymore :-(
>
What about disconnecting network cable (or modifying routing tables)
while some output is going from remote machine and then killing
ssh session on client and starting another one?

> Could this be related to a (possible) bug in the m68k IPv4 checksum code?
> But then, the first time I saw the problem, it was between two ia32 boxes
> running 2.0.x, more than one year ago.
>
> Anyone with a clue? Thanks!
>
> Greetings,
>
> Geert
>
> --
> Geert Uytterhoeven Geert.Uytterhoeven@cs.kuleuven.ac.be
> Wavelets, Linux/{m68k~Amiga,PPC~CHRP} http://www.cs.kuleuven.ac.be/~geert/
> Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium
>
It was perhaps not much help,

just wanted to share my experiences.

Best regards,

Wojtek
Wojtek.Pilorz@bdk.pl


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