Gratuitous ARP

ARP (Address Resolution Protocol) request to its own IPv4 address as the target address is called gratuitous ARP.

Use case:

1. Duplicate address check
   • If there is another ARP reply that's not the host for the same IP address then you know it's duplicated.
2. ARP cache update.
   • When a device receive ARP request of the same IP in the ARP Table, it will update the hardware of that entry.

It is disabled in IOS but can be enabled using ip gratutious-arps