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Old 03-19-2010, 07:38 PM
Alan McKinnon
Default SSH sessions hanging in VPN

Hi all,

Not really directly related to Gentoo except that the workstation where it
happens is a Gentoo machine :-)

Our VPN at work is a Juniper Secure Connect. I tend to have many konsole tabs
running ssh at one time, as well as IMAP connections to Exchange and several
browsers tabs to intranet sites. Occasionally, and apparently triggered
randomly[1], all existing ssh sessions freeze and never come back (even after
several hours). The connections are still up and do not die on the remote end.
Mail connections stay up and the browser tabs continue to work as well[2].

I know the ssh sessions are alive on the other end as I can immediately log in
in another konsole tab and that works just fine. Even after several hours the
first sshd process does not timeout (timeouts are enabled). So it would seem
that it's the return path going tits up. My next step is going to be running a
trace and tcpdump on one of those existing session next time it happens.

Meanwhile, and this is my real question, how would I go about sensibly
debugging this in a methodical manner? I'm going to have to get my security
guys and routing guys to investigate but they will need real information to
work with. Everything I can think of just reduces to throwing brown smelly
stuff at the wall and hoping some of it sticks.

[1] By randomly I mean sometimes 4 times a day, sometimes nothing for several
days. I have not seen a correlation to anything I'm doing that might trigger
[2] This is expected as HTTP is sessionless.

alan dot mckinnon at gmail dot com

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