two networks in one server?

Matthew Seaman m.seaman at
Sun Oct 9 11:38:30 UTC 2011

On 09/10/2011 10:36, pepe wrote:
> I'm just asking before trying if it possible to use two network uplinks in
> one server so other would be just backup way in?
> I have currently connection from two ISPs and server is up with one
> connection. Is it possible to add another nic and wire that to connection
> from another isp? So isp 1 would be in normal use in/out, but isp 2 could be
> used connecting in?

This is a very commonly asked question around the Internet.

The answer is -- it's a lot harder to do properly than you might think.
 Requires understanding Internet routing protocols like BGP and you will
need the cooperation of both ISPs to make it all work.

However there is a "light" version which might work for you.  Keywords
here are "policy based routing."  In this case you can use firewall
software to forward packets by an alternate gateway.  This only affects
the outward path from your system: no good at all if all the incoming
traffic is using an uplink that fails, but you can use it to load
balance across multiple links.



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP:     Ramsgate
JID: matthew at               Kent, CT11 9PW

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