Multiple default routes, same subnet

[Fernando Lozano]

Hi,

I have two internet links, from different ISPs for my office network, 
each one with it's own router (which is a linux PC) so I don't loose 
internet connectivity easily. One ISP has a much higher bandwitch, so 
usually all my computers use it as the default gateway. The other one is 
intended as a contingency link.

Today I have to manually change the default gateway on all computers 
when the main link goes down. I want an automated way to do this.

All how-to's I could find on google were such as:
http://www.generationip.com/documentation/network-documentation/93-howto-setup-multiple-default-gateway-on-linux

Where they use iproute2 so a single router/computer can switch between 
two internet links. While I can undersand this scenario, the single 
computer becomes a single point of failure. I don't want to setup a 
"cluster" using heartbeat, cluster suite and similars just to provide a 
router failover. It looks overkill.

Other problem, all iproute2 samples I find thave those two gateways on 
different subnets and use the source address to route properly and avoid 
problems like "onion routing".

I'd like to have two routers/computers on the same subnet, each one 
connected to it's own internet link, and have the network computers 
switch from the main one to the contingency one when needed.

So a computer would have two default gateways on the same subnet.  I 
can't find how to change the iproute2 samples setup so the gateways can 
be on the same subnet and everything works. I allways end up having all 
traffic going though one link and when it fails I loose internet 
connectivity.


[]s, Fernando Lozano