[Durham] Fwd: Port forwarding via two ADSL lines

Martin Ward martin at gkc.org.uk
Wed May 25 17:06:14 UTC 2011

I have just had another ADSL line installed. Both lines have
a static IP address, so I decided to set up port forwarding
on both routers to the same machine (my main file server).
The idea is that if one ISP goes down, I can still access my home
machine via the other ISP by using the other IP address:
and similarly email will still get through if I set the new IP address
as a backup MX host.

But this doesn't work: it seems that the server will only accept
forwarded connections that come in through its default outgoing route.

If I do:

route del default
route add default gw IP-OF-OLD-ROUTER

then I can ssh in via OLD-IP-ADDRESS, but not NEW-IP-ADDRESS

If i change the default route:

route del default
route add default gw IP-OF-NEW-ROUTER

then I can ssh in via NEW-IP-ADDRESS but not OLD-IP-ADDRESS.

Both routers are port forwarding ssh to the internal IP address
of the server.

Is there a way to tell the server to accept incoming connections
from both routers?


STRL Reader in Software Engineering and Royal Society Industry Fellow
martin at gkc.org.uk  http://www.cse.dmu.ac.uk/~mward/  Erdos number: 4
G.K.Chesterton web site: http://www.cse.dmu.ac.uk/~mward/gkc/
Mirrors:  http://www.gkc.org.uk  and  http://www.gkc.org.uk/gkc

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