5. LVS: The ARP Problem

Another LVS note, in case I would forgot this. This is from http://www.austintek.com/LVS/LVS-HOWTO/HOWTO/LVS-HOWTO.arp_problem.html

5. LVS: The ARP Problem: "2.4.26 and 2.6.4 will come with 2 new device flags for tuning the ARP stack: arp_announce and arp_ignore. All IPVS like setups can use arp_announce=2 and arp_ignore=1/2/3 to solve the 'ARP problem' with DR/TUN setups. These flags are going to replace the 'hidden' functionality which does not work well for directors when they are changing their role between master/slave for a particular VIP. The risk is that other hosts can probe for VIP using unicast packets for which the hidden flag always replies. I'll continue to support the hidden flag for 2.4 and 2.6 to help existing setups but switching to the new device flags (or other solutions) is recommended.

Documentation is in the 2.6 kernel docs (linux/Documentation/networking/ip-sysctl.txt).

arp_ignore: 1 - reply only if the target IP address is local address configured on the incoming interface. if eth0/arp_ignore=1 then all IPs on eth0 are replied, all others (on lo) are not."