Tunnel Routing Question

M

mlager

I have a pretty simple setup... Two locations, each with a FreeBSD endpoint that have a GIF tunnel built between them:

Router A:
External: A.A.A.A
Internal: 172.16.1.1

Router B:
External: B.B.B.B
Internal: 172.16.2.1

From behind router A, I can access the 172.16.2.0/24 network, and from behind router B, I can access the 172.16.1.0/24 network.

Now for my question... If I have a device behind router A that is sitting on the 172.16.1.0/24 network, is there a way to have that devices Internet traffic go through router B? Something to the effect of a device behind router A having an IP address of 172.16.1.100 but a default gateway of 172.16.2.1? Not sure if that's possible, but I appreciate any feedback.
 
Make a tunnel between router A and B. Host on 172.16.1.0 still points to 172.16.1.1 as its default gateway. It's up to router A to route over tunnel to router B and internet (via static route or dynamic protocol). Treat tunnel as just another physical interface.
 
That makes sense, but what would a static route on router A look like to route a specific device behind router A through router B, lets say with an IP address of 172.16.1.100 and a default gw of 172.16.1.1... Keeping in mind that I only want traffic for the client 172.16..1.100 to router through 172.16.2.1 and everything else remain the same?
 
Routing table lookups are performed on destination address, not source address. What you want is source routing, aka policy routing. Linux has a policy routing framework, but in FreeBSD you have to use a firewall to do it.

ipfw(4) and pf(4) can both alter the nexthop of IP packets. Have a look at fwd in ipfw(4) or route-to in pf(4).
 
Keep in mind that router B needs to be told to route over GRE tunnel as well, unless you want another path.
 
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