Default gateway changing but ARP cache does not timeout

graham-lewis · ‎10-23-2008

Hi,

I'm planning to migrate a subnet off some old kit running VRRP onto two new Catalyst 6509s with HSRP. I tried a similar change last week but had an issue with the ARP cache on some hosts not picking up the new MAC address of the HSRP VIP address, i.e. not timing out, even after 24 hours. It's not possible to ping the hosts with the HSRP VIP address, only the real addresses of the interfaces. I was thinking of setting up a router with the default gateway address and changing the BIA of the ethernet interface to HSRP VIP (in this case 0000.0c07.ac3c) then running a broadcast ping. The problem is not all hosts respond to the broadcast ping, will they update their ARP caches anyway or can you think of a better workaround?

Thanks

mchin345 · ‎11-02-2008

An ARP reply is generated only if the destination protocol IP address is reachable from the local host, as determined by the routing algorithm, and the next hop is not through the same interface. If the local host functions as a gateway, this can result in ARP replies for destinations not in the same subnet. This shows that to drop the ARP request is justifiable.

Troubleshoot Address Resolution Protocol (ARP) or Content Addressable Memory (CAM) table-related issues on Catalyst 6500/6000 Switches.

For further information click this link.

http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00807347ab.shtml#dfc