Stopping internal forwarding

[dmh2000]

If I have a machine with two NIC's, each with having an IP on a different subnet than the other, and I send a message from one of the IP's to the other one using either TCP or UDP; is there a way to force the packets to be routed out of the machine first and let some external system route it back to the destination.

So far I haven't found a way to get it to go to an external router for forwarding. I realize this is an odd situation, but anyway; can it be done...

 

[AndyBo]

Let's say you want to route from NIC 1 to NIC 2. The only way I can think that might work would be to setup a static route from NIC 1 IP address to NIC 2 IP address via the external router.

I'm not sure I see the logic of doing this, though - what are you trying to accomplish?

 

[dmh2000]

I have tried to statically route the packets in the routing table, but the packets still never leave the machine. It appears that the routing table is never consulted in the matter. I've also wondered if Solaris figures out that it is on the machine and never tries to send it out. It would be nice to see how multiple NIC's under Solaris can be modeled in a network diagram, or whether it really would fit that paradigm, because there could be some preemptive forwarding going on.
Anyway, I'm just trying to see if I need to get another machine to test an external device, or if I can do it with just one.

 

[AndyBo]

It sounds like it's doing what I suspected it would. Unix in general doesn't send TCP/IP packets out to the external network if it knows that the IP address it is sending to is a local address. I guess it's an efficiency thing. It's also something to remember when testing your server network connectivity - pinging the local IP address will not test the network you are connected to. Instead, Unix will just say "Yep - I can talk to that IP address because it's my own."