[CentOS] CentOS 4.x - Multiple gateways

[Charles Lacroix]

On Thursday 25 May 2006 08:35, Joshua Gimer wrote:
> There isn't going to be a difference to your routing. Whatever gateway
> comes first in your routing table is going to be used first. You can add
> the one that you want to use as the primary gateway in ifcfg-ethx of your
> first interface. Then you should see two entries in your routing table
> (along with the usual entries and information):
>
> Destination
> Gateway                                                   Genmask
> Interface
> 0.0.0.0               (The address of your first gateway)
> 0.0.0.0           eth0
> 0.0.0.0               (The address of your second gateway)
> 0.0.0.0
> eth1
>
> On 5/25/06, Tom Brown <tom at ng23.net> wrote:
> > Hi
> >
> > On a multihomed box how can i set different gateways for each NIC?
> > Setting them in the ifcfg-ethx does not seem to make any difference to
> > the routing?
> >
> > thanks
> > _______________________________________________
> > CentOS mailing list
> > CentOS at centos.org
> > http://lists.centos.org/mailman/listinfo/centos

Hi, 

I've done some work on this a few month ago at my other job, and basically
the solution lies in iproute2 commands.

First you need to create a rule and assign that traffic to a different table 
than the main table. Then you can easily add a default route to that new 
table.

so it would look like this

ip rule add from 192.168.1.0/24 table X 

check /etc/iproute2/rt_tables if you want to make aliases like eth1 eth2 eth3 
it will get easier if you automate this thing :)

After that you set a default route to this new table.

ip route add default via 1.2.3.4 table X


Once you have this done and working it's a matter of getting your
dhclient of pppoe to do this for you as soon as ip changes.

for pppoe create a /etc/ppp/ip-up.local script.
for dhclient stuff you need to look in /sbin/dhclient-script script to find 
out how it will execute what's in /etc/dhclient-enter-hooks 
or /etc/dhclient-exit-hooks

It's quite useful and for me it did turn out to work nicely. I just had to 
create some sort of master script that would take decisions on what's going 
on with my gateways :) It was pretty fun to work on that. I hope this helps 
you out.

Later,
Charles