Multiple default routes, same subnet

[Bill Davidsen]

Fernando Lozano wrote:
> 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.
>
I went another way on that, but it seems to me the solution is to just set the 
metric to the route you want most of the time lower that the "fallback" routeer. 
Define a route to each router, then set the default routes. Actually I think the 
order won't mater. If you use "ip route" the "peer" option might be useful, I 
haven't done this in a while!

> 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
>


-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot