Some history.

I have a working 2.4.20 kernel (slackware) on an old box with 5 pci ethernet cards.

I went to upgrade and getting 5 ethernet ports was a hassle with the disappearing pci slots in new computers so I tried the asix usb devices (four of) with a 2.6.16.9 kernel. It failed ... it seemed to send bogus spanning tree packets (funny mac addresses) which the hub (managed) didn't like and the hub turned off the port.

So, I tried a tulip card. Same bogus spanning tree packets. Seems like it's not the card driver.

2.4.20 doesn't support the new hardware so I bought a Dlink 580TX (4 ports on one pci card) and compiled in the 2.4.32 kernel. So far so good. Now with ethereal that the arp responses are coming from all four mac addresses on the dlink, I'm sure that's going to cause some trouble. How do I configure it NOT to do arp responses on devices that do NOT have the ip address matching the arp request? Perhaps it's dumb to even ask ... ?

Oh, the on board gigabit card also responds, the following from ethereal ...
Address Resolution Protocol (request)
Sender MAC address: 00:08:0d:1e:e6:c3 (192.168.1.49)
Sender IP address: 172.18.10.49 (172.18.10.49)
Target MAC address: 00:00:00:00:00:00 (00:00:00_00:00:00)
Target IP address: 172.18.10.50 (172.18.10.50)

Address Resolution Protocol (reply)
Sender MAC address: 00:13:72:11:3b:a9 (172.18.10.50)
Sender IP address: 172.18.10.50 (172.18.10.50)
Target MAC address: 00:08:0d:1e:e6:c3 (192.168.1.49)
Target IP address: 172.18.10.49 (172.18.10.49)

Address Resolution Protocol (reply)
Sender MAC address: 00:0d:88:68:89:9d (D-Link_68:89:9d)
Sender IP address: 172.18.10.50 (172.18.10.50)
Target MAC address: 00:08:0d:1e:e6:c3 (192.168.1.49)
Target IP address: 172.18.10.49 (172.18.10.49)

Address Resolution Protocol (reply)
Sender MAC address: 00:0d:88:68:89:9c (D-Link_68:89:9c)
Sender IP address: 172.18.10.50 (172.18.10.50)
Target MAC address: 00:08:0d:1e:e6:c3 (192.168.1.49)
Target IP address: 172.18.10.49 (172.18.10.49)

Address Resolution Protocol (reply)
Sender MAC address: 00:0d:88:68:89:9f (D-Link_68:89:9f)
Sender IP address: 172.18.10.50 (172.18.10.50)
Target MAC address: 00:08:0d:1e:e6:c3 (192.168.1.49)
Target IP address: 172.18.10.49 (172.18.10.49)

Address Resolution Protocol (reply)
Sender MAC address: 00:0d:88:68:89:9e (D-Link_68:89:9e)
Sender IP address: 172.18.10.50 (172.18.10.50)
Target MAC address: 00:08:0d:1e:e6:c3 (192.168.1.49)
Target IP address: 172.18.10.49 (172.18.10.49)

I think I've found it, in ls /proc/sys/net/ipv4/conf/... arp_ignore and arp_announce. It's also in Documentation/networking/ip-sysctl.txt in the kernel build tree.

This is known as arp-flux problem. See section 2.1.4. of the "Guide to IP Layer Network Administration with Linux" for more details. But yeah, the sysctl options you mentioned are one possible solution.

Thanks. In the end I put the followig in rc.local, works nicely.

for i in all eth0 eth1 eth2 eth3 eth4 ; do echo 1 > /proc/sys/net/ipv4/conf/$i/arp_filter; done