> I have a PPPoSSH VPN running between two linux machines, one behind an M11
> and the other behind an MW1122. I can create the connection fine, and
last
> week the link stayed up the whole week with no problems.
>
> However this week every hour or so the link seems to just freeze, both
ends
> think the ppp session is still active, however I can't ping either end
from
> the other.
>
> Has any got any ideas? I haven't changed anything so I don't know why it
is
> now doing this!
>
> Regards,
>
> Aaron Martin

Hi Aaron,

    There is a fundamental flaw with tunneling tcp connections via tcp-based
tunnels such as ssh due to a race condition which can occur during periods
of congestion. The TCP retry timer algorithms don't cascade - you have one
timer running for the tunnel, and another for the tunneled TCP packets.
Sorry folks, it doesn't work reliably - don't use TCP based tunnels via SSH,
it's not reliable and never will be!

Brent Russell,
Department of Physics,
University of Otago.

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Received on Fri Jan 5 23:26:45 2001