Messages in this thread | | | Date | Fri, 19 Mar 2004 10:16:36 +0100 | From | Helge Hafting <> | Subject | Re: 2 nics in the same machine... |
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RANDAZZO@ddc-web.com wrote: > I have connected two nics in the same machine with a null modem cable... > > I have configured nic 1 to be 156.15.16.1 and nic 2 to be 156.15.16.2 > > I have adjusted the routes so that nic 1 routes to nic 2 and vice versa... > > how come when I ping 156.15.16.1 it does not go out nic 2... > > am I missing something?
Kernel sees that it have a ping packet destined for 156.15.16.1 Kernel notices it has several NICs available, so it chooses the one closest to the destination. NIC1 _is_ 156.15.16.1 so it _is_ the destination. Kernel figures that the packet is already here, and never sends it out on the wire.
A crossed cable between two NICS in the same machine is a testing setup, right?
If you want to test NICs (or cables & hubs) do this:
1. Run a packet sniffer on the "listening" NIC. Run it in promiscuous mode so it'll even sniff packets not meant for it.
2. Set a default route to the "sending" NIC. Or at least a route to some network that isn't on your machine.
3. Ping the remote network. You will not get an answer, but: The packet will be sent through the "sending" NIC, and sniffed by the "listening" NIC. So you'll verify that NICs and cable works. Optionally make a script that reverses the roles of the two NICs if you want to test both ways.
If, on the other hand, you're testing apps/protocols, don't worry that the traffic don't hit the wire. A test utilizing internal loopback is just as good. If you really need traffic to go out on a wire, then you likely need two or more machines for a realistic test too.
Helge Hafting
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