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Gratuitous ARPs do not populate the router ARP Table



In order to debug an ARP problem in a Firewall cluster environment, I connected a one-armed router on the public VLAN of the firewall cluster, in order to observe the ARP cache behaviour during a switchover. I configured a loopback interface on this router and  a default route to this loopback interface to simulate a real router.

When a switchover occurs between firewall cluster members, the active member sends Gratuitous ARPs for all NATed IP addresses. In my environment, I have 110 NATed addresses configured on the firewall.

By launching a "debug arp" on the one armed router,  I clearly see all 110 gratuitous ARPs arriving on the router, but the ARP cache of the router is NOT populated with the 110 entries...

Note  : The command is configured on the one armed router :

Router(config)# ip arp gratuitous local


What can be the problem ? Is there any condition for a router to accept Gratuitous ARPs ?


Thank you for any help





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