How to elegantly handle two ISPs on a single box?

Marc Haber mh+netfilter at
Wed Apr 6 21:46:35 CEST 2005

On Wed, Apr 06, 2005 at 02:14:24PM -0500, Taylor, Grant wrote:
> You might try Equal Cost Multi-Path (ECMP) routing.

That will have me send out packets with source A to ISP B and vice
versa which will have the packets killed by the ISPs reverse path

> Give this a shot and see what happens.

I don't need to try this, it will end up with pretty much exactly 50 %
packet loss.

> You will just need to make sure that you do something like the following in
> your nat / POSTROUTING chain:
> iptables -t nat -A POSTROUTING -o <dev of ISP B> -j SNAT --to-source
> iptables -t nat -A POSTROUTING -o <dev of ISP A> -j SNAT --to-source

This will NAT the first, third, fifth packet of a TCP session to and the second, fourth and sixth packet of the same
session to I seriously doubt that the session will come up
at all.

I am either completely missing the poing or your suggestion is making
things worse.


Marc Haber         | "I don't trust Computers. They | Mailadresse im Header
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