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SubjectMultiple Interface problem with ARP (eth0/eth1, eth0/lo)
If you have multiple interfaces on one network (not unusual in switched
environments), ARP requests will produce replies for each MAC address.

This could easily cause performance problems in some circumstances: If you
run different IP addresses on each interface and use that to partition
traffic, you will be foiled because the traffic will bounce from MAC address
to MAC address everytime there is an ARP.

This is probably related to the eth0/lo ARP problems but possibly not. It
very well may be that both interfaces respond because they both see a
broadcast request.

While I can understand situations where you have ethernet ports on different
networks and you want to respond with both IP's on both networks, you really
should give preference to the card that owns the address and suppress the
ARP from the other card somehow when it is in fact the ARP request. Too bad
ARP doesn't have priority... Then you could arp reply with 1 hop vs. 0

Maybe a solution is to test whether multiple controllers can talk to each
other or not to detect whether they are on separate networks. Or just make
it configurable to get it when you need it.

Debug with two ethernet controllers and arpwatch, or let me know what I'm
not understanding.

OptimaLogic - Finding Optimal Solutions
Web/Crypto/OO/Unix/Comm/Video/DBMS Stephen D. Williams Senior Consultant/Architect
43392 Wayside Cir,Ashburn,VA 20147-4622 703-724-0118W 703-995-0407Fax

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