Configuring Gratuitous ARP

Gratuitous Address Resolution Protocol (ARP) requests provide duplicate IP address detection. A gratuitous ARP request is a broadcast request for a routing platform’s own IP address. If a routing platform sends an ARP request for its own IP address and no ARP replies are received, the routing platform’s assigned IP address is not being used by other nodes. If a routing platform sends an ARP request for its own IP address and an ARP reply is received, the routing platform’s assigned IP address is already being used by another node.

By default, the routing platform responds to gratuitous ARP requests. On Ethernet interfaces, you can disable responses to gratuitous ARP requests. To disable responses to gratuitous ARP requests, include the no-gratuitous-arp-request statement at the [edit interfaces interface-name] hierarchy level:

To return to the default—that is, to respond to gratuitous ARP requests—delete the no-gratuitous-arp-request statement from the configuration:

Gratuitous ARP replies are reply packets sent to the broadcast MAC address with the target IP address set to be the same as the sender’s IP address. When the routing platform receives a gratuitous ARP reply, the routing platform can insert an entry for that reply in the ARP cache.

By default, updating the ARP cache on gratuitous ARP replies is disabled on the routing platform. On Ethernet interfaces, you can enable handling of gratuitous ARP replies on a specific interface by including the gratuitous-arp-reply statement at the [edit interfaces interface-name] hierarchy level:

To restore the default behavior, include the no-gratuitous-arp-reply statement at the [edit interfaces interface-name] hierarchy level:

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