I have a server that has 2 network cards connected to two different networks.

I've configured rc.inet1.conf to have eth0 on a private network, and eth1 to be on a public network.

There is only one line "Default Gateway IP Address". Each network card has it's own gateway however.

How do I configure each card for each network?

I tried just adding lines to each card eth0 and eth1 as :

GATEWAY[0]="X.X.X.X" and GATEWAY[1]="1.1.1.1" but that doesn't seem to work.

If I change the default gateway line to the gateway IP for the public network, the public network works, but private does not.

If I change the default gateway line to the gateway IP for the private network, the public network does not work, but the private does.

How do you set up separate gateways for each network?

James

You can only have one default gateway on your system, even if it is connected to multiple networks.

When your networking is set up, aside from a default gateway (assuming you have one configured), each network gets a route added for it. It's those routes which configure how your host sends packets destined for each network - packets for your private network on one interfaces, and public on another.

The default gateway is used when your host needs to send packets to a network it doesn't know about.. eg, the internet.

If you have two routes out to the internet, you can only have one of them as your default. You'll need to use routes to determine which gateway is used for accessing different networks.

HTH.

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That's called routing.

A Default Gateway, also known as "a gateway of last resort", is just the most general route possible, covering every IP network in existence. Adding two such routes pointing to different gateways will result in round-robin load balancing at the packet level, which is not what you want.

However, specific routes always take precedence over more general routes. What you need to do for this to work, is to add a more specific route to your private network via the other gateway (router). You do this using the ip route add command (or route add on older systems).

For instance, if the network 192.168.10.0/24 can be reached via gateway 192.168.1.2, the command would look like this: ip route add 192.168.10.0/24 via 192.168.1.2

Such static routes (as they are called) become part of the kernel routing table and take effect immediately, but as with other IP parameters they are lost at reboot. Slackware doesn't have an init script for storing static routes, but you could always add the relevant command(s) to /etc/rc.d/rc.local.

add a private route on eth1, the nic connected to the public network.

if the private network is 10.10.10.0 with a /24 subnet (mask 255.255.255.0) then

to add the route:
to remove the route:
Have fun!

I've played around with this earlier some years ago, it's possible to use multiple default gateways with different metrics.
I can't really remember how it's done but it's possible. Your program has to bind to the source ip address when doing certain things.. :-)

It might be right to look into source routing, which probably will get you there.

Nope, the gateway with the lowest metric will always be used.
You might be thinking of policy routing, but that's not what the OP needs/wants.
That's another thing entirely, and also not what the OP is looking for.

Yeah you're right about the metrics.
Was digging and found this...

Perhaps something else..