[Durham] Port forwarding via two ADSL lines

Richard Patterson Richard at helpquick.co.uk
Wed May 25 20:10:52 UTC 2011

> -----Original Message-----
> From: Martin Ward [mailto:martin at gkc.org.uk]
> Sent: 25 May 2011 17:55
> To: durham at mailman.lug.org.uk
> Cc: Richard Patterson
> Subject: Fwd: Port forwarding via two ADSL lines
> 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.

I assume you have both routers on the same network, such as the first router has say, and the second on, with your server being 

If on the server, you add an IP alias such as (ifconfig eth0:1 then you can add another default route via the alias interface eth0:1 (route add gw dev eth0:1)

You should then find that connections coming in on eth0:1 will go back out on eth0:1

Give it a try and let us know how it pans out...



Richard Patterson
Mobile: 07921 512 459

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