I have an old Linux machine running a 2.4.37 kernel. In the machine are two NIC cards both on the same network with different IPs. For some testing, we want each IP's traffic routed through that NIC, but what is actually happening is all the traffic for both IPs is getting routed through one of the ethernet devices and the other is unused. If I take another machine on the network with an empty ARP Cache and ping both IPs, and then check the ARP Cache, I see that it has the MAC for one of the two NICs under both IPs. Basically the Linux box is allowing both NICs to respond to ARP requests for each other- which is the default behaviour. However, I have arp_filter enabled for both NICs which is supposed to eliminate this from happening, but appears to have no effect. I've also tried disabling rp_filter, but that seems to have no effect either. Here are my relevant sysctl entries:
net.ipv4.conf.eth1.arp_filter = 1 net.ipv4.conf.eth1.rp_filter = 0 net.ipv4.conf.eth0.arp_filter = 1 net.ipv4.conf.eth0.rp_filter = 0 net.ipv4.conf.lo.arp_filter = 1 net.ipv4.conf.lo.rp_filter = 0 net.ipv4.conf.default.arp_filter = 1 net.ipv4.conf.default.rp_filter = 0 net.ipv4.conf.all.arp_filter = 1 net.ipv4.conf.all.rp_filter = 0
I find tons of links to people with the same problem on google, but once they set arp_filter=1 the problem goes away for them, but not for me.
Edit: I've also been playing with various arp_ignore and arp_announce settings, but no matter what I do I can't get each interface to only respond to ARPs for its own IP