[Gllug] Ssh Debugging

Andrew Farnsworth farnsaw at stonedoor.com
Tue Feb 28 10:05:03 UTC 2012

On Tue, Feb 28, 2012 at 10:23 AM, James Courtier-Dutton <
james.dutton at gmail.com> wrote:

> On 28 February 2012 07:45, t.clarke <tim at seacon.co.uk> wrote:
> > Re ssh bind to port 1234 problem;
> >
> > I have only taken a brief glance at this thread,  but it seems to me
> that if
> > the server is saying it cannot bind to the port, there are only really
> three
> > possibilities:-
> >
> > 1 - most likely - another process is bound to the port;  the netstat -p
> command
> > I believe will show which processes are bound to which ports.
> >
> > 2 - the server is giving a misleading message; I would imagine it can be
> placed
> > in full debug mode to capture messages as to exactly what it is doing
> (maybe
> > possible to trace the system calls?)
> >
> > 3 - something wrong with the kernel's IP stack  (highly unlikely!)
> >
> But, I don't think this is a configuration problem at either end.
> The OP said the ssh link goes down 5-6 times a day, so it works most
> of the time.
> The only thing that has changed is the WAN link.
> The binding problem is most likely a red herring.
> My guess is that the real problem is most likely to be due to some
> deep packet inspection/policy being applied by the ISP.

It could also just be a much simpler "drop all connections after XXX
minutes" configuration in the ISP (or middle tier ISP).  I would try
logging around this and see if all the disconnect times are approximately
the same number of minutes after the connect occurs.  If this is the case
you can either raise it with the ISP to get it fixed (good luck), switch
ISPs, or code around it.

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