Persistent SSH sessions

[Damien Miller]

On Mon, 2 Aug 2010, Mukund Sivaraman wrote:

> Hi all
> 
> I have an ADSL modem which reboots when there is a power cut and the
> inverter (UPS) kicks in.  Internet access is down for a duration of 1
> to 2 minutes while the modem boots.
> 
> I have many SSH tunnels and shells active.  Due to the default
> "TCPKeepAlive On" setting, these sessions are terminated almost
> immediately.

This is almost certainly not due to TCP keepalives, which are generally
send pretty infrequently and don't kill sessions anyway.

It is much more likely that your modem is using NAT and loses its
NAT state table on reboot and is unable to associate the outside and
inside halves of your connections, gives up and sends a TCP RST to
each.

If this is the case, then no amount of configuration in ssh/sshd will
help you unfortunately. 

-d