CentOS - May 2006 - CentOS 4.x - Multiple gateways

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

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
>


-- 
Thx
Joshua Gimer
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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

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On Thu, May 25, 2006 at 11:51:14AM +0100, Tom Brown
wrote:
> 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?
What are you trying to accomplish ? Load balancing ? Redundancy ?

- -- 
Rodrigo Barbosa <rodrigob at suespammers.org>
"Quid quid Latine dictum sit, altum viditur"
"Be excellent to each other ..." - Bill & Ted (Wyld Stallyns)

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Le Jeudi 25 Mai 2006 12:51, Tom Brown a ?crit?:
> 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
Hello,

  I think setting /etc/sysconfig/network-scripts/route-ethX files will help,
see http://blog.subverted.net/?p=571

Tom Brown 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
Try creating routing tables per NIC, populating those tables and 
creating ip rules to lookup the respective table. This means you need to 
identify which NIC the packets belong to. You can try adding rules to 
the mangle PREROUTING chain of netfilter to mark the packets based on 
their source ip. Then the ip rules can instruct the kernel to lookup the 
proper routing table depending on the firewall mark.

man ip, man iptables, http://linux-ip.net/html/routing-tables.html and 
http://linux-ip.net/html/tools-ip-route.html