Messages in this thread | | | Date | Sat, 20 Mar 2004 19:42:52 +0100 | Subject | Re: 2 nics in the same machine... | From | Helge Hafting <> |
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On Fri, Mar 19, 2004 at 11:36:56PM +0100, Willy Tarreau wrote: > Hi, > > On Fri, Mar 19, 2004 at 10:16:36AM +0100, Helge Hafting wrote: > > > 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. > > Nearly right. He will need to enter static ARP entries for this to > work because his host will try to resolve the gateway's address first, > so nothing except ARP will go out. > I didn't think of that. Of course, capturing an ARP broadcast is probably good enough for testing cables. One might want better than that for testing the NIC driver though.
> DNAT out + SNAT in may be OK. I've used this setup in the past, but didn't > not go on because of performance problems. Now, Julian Anastasov has written > a wonderful patch named "send-to-self" which does the trick automagically. > You can get it on his site ( http://www.ssi.bg/~ja/ IIRC ). > > > 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. > > Right. Except that in some very weird cases, the higher MTU on loopback may > affect the app's behaviour (less packets, or bigger reads at once, etc...).
ifconfig lo mtu 1500 :-)
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