Force Packets onto Wire

[Tony Dal Santo <tmd@xxxxxx>]

Greetings,

I'm trying to use a single Linux box to test a router.  The Linux box has multiple ethernet cards in different subnets.  When trying to send from one subnet to the other, Linux of course bypasses the external network.  This doesn't test the router much!  I'm looking for a way to force the packets out one NIC, through the router, and back in the other NIC.  Ideally, I'd still like to use regular commands (ping, ttcp), and not have to create my own packets.

While searching the web, I see this had been addressed in kernel 2.0 with a change by Brian Moyle to arp.c (which Alan Cox thought was unwise to adopt for the general distribution).  I was wondering if anything similar has been done in the 2.4 code.  Or can I use the advanced routing features and somehow coax Linux (e.g. via different TOS) that for some/all traffic, the external interface is better.

I've played around with the "ip route" and "ip rule" commands, but don't yet have a sufficient understanding of the routing internals to do what I want.  Any assistance in this area would be appreciated.

Thanks,
Tony