Connecting two networks with two linux boxes.

I have 2 networks each with a linux box as the gateway to the internet.

At the moment they are VPN'd together, but are close enough to get a
cable run and I'd like to connct them like this to make it quicker
so each linux box will have 3 nics in it.

My question is possibly a dumb one! But what should the IP for the 3rd
nic in each box be?

The networks are:
network - linux box internal address
Box 1) 10.0.12.x/24 - 10.0.12.1
Box 2) 192.168.12.x/24 - 192.168.12.1

Should the 3rd NIC in the box 1 be on the 192.168.12.x range, and vice
versa but wouldn't that confuse the other network as it would think that
it is a local IP when it wouldn't be.

Should they both be on a different range althogether? And then set the
routing up on each.

ie 3 NICS in each
Box1
internal 10.0.12.1
public 123.456.78.2
"intranet" 10.0.13.1

Box2
internal 192.168.12.1
public 423.243.123.32
"intranet" 10.0.13.2

If it was 2 networks with one linux box it would be easy, just not sure
how you'd connect the two boxes together....

Any advice appreciated!

Cheers

Mark

Markvr wrote:
> I have 2 networks each with a linux box as the gateway to the internet.
>
> At the moment they are VPN'd together, but are close enough to get a
> cable run and I'd like to connct them like this to make it quicker
> so each linux box will have 3 nics in it.
>
> My question is possibly a dumb one! But what should the IP for the 3rd
> nic in each box be?
>
> Should they both be on a different range althogether? And then set the
> routing up on each.

That should work.

Markvr wrote:
> I have 2 networks each with a linux box as the gateway to the internet.
>
> At the moment they are VPN'd together, but are close enough to get a
> cable run and I'd like to connct them like this to make it quicker
> so each linux box will have 3 nics in it.
>
> My question is possibly a dumb one! But what should the IP for the 3rd
> nic in each box be?

On a separate subnet from the other two interfaces.
All you have to do to make routing work is, on each box, add a static
route to the original internal network on the *other* box, with the IP
of the other boxes' 3rd interface as the gateway for that static route.

Box 1:
$INTERNAL1, $NEW_IF1 = 10.0.0.1 (or whatever)

Box 2:
$INTERNAL2, $NEW_IF2 = 10.0.0.2

On Box 1:
route add net $INTERNAL2 gw $NEW_IF2

On Box 2:
route add net $INTERNAL1 gw $NEW_IF1

Done.

> If it was 2 networks with one linux box it would be easy, just not sure
> how you'd connect the two boxes together....

Exactly as if there was no Internet - whether you have 3 interfaces or
28, it's all the same.

J