Idle SSH session disconnects

Jani Jaakkola jjaakkol at cs.Helsinki.FI
Sat Aug 31 23:06:45 EST 2002

On Fri, 30 Aug 2002, Peter Stuge wrote:

> On Fri, Aug 30, 2002 at 01:33:55PM -0700, Jim Cunning wrote:
> > Can anyone help explain this situation?
> Are both client and server Linux boxes?  If some other less robust TCP/IP
> stack is involved this might be the cause for connectivity loss.

I have never known about any Linux version, which would be non robust 
enough to cut TCP/IP connections. However, with a stateful firewall this 
is easy achieve (regardless of the OS the firewall might have), so my 
guess is that the problem is caused by some firewall/router/nat 

> Have you tried playing with KeepAlive or maybe ClientAliveInterval and
> ClientAliveCountMax in sshd_config?

Yup, client-alives could force the firewall to keep TCP-connections alive.
But then again might not; keepalives sent by the server can also force the 
TCP-connection closed, if the network is down for few minutes (and it 
might take some time for the client to notice that the connection 
has been forced closed).

Anyway, I'm sure that this is somekind of network problem, not an openssh 
or OS problem. And it seems that Frank Cusack already wrote a better 
analysis than I did.

- Jani

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