Technical Tip: Setting the number of Gratuitous ARP (GARP) packets sent and their interval by the primary unit

It is possible to use the following command to set the number of gratuitous ARP packets that are sent after a failover.

Command syntax.

config system ha
    set gratuitous-arps <enable / disable ; default enable> 

 set arps <1 to 60; default 5>

 set arps-interval <1 to 20; default 8>

end

Gratuitous ARP (GARP) packets are sent when a cluster unit becomes a primary unit.

The gratuitous ARP packets configure connected networks to associate the cluster virtual MAC address with the cluster IP address.

• gratuitous-arps: Enables sending of gratuitous ARP packets. If link-failed-signal is enabled, GARP needs to be disabled. 
• arps -> Set the number of gratuitous ARP packets sent by the new primary unit after HA failover. Lower it to reduce traffic. Keep it higher to reduce failover time.
• arps-interval -> Time between gratuitous ARPs. Lower the interval to reduce failover time. Keep it higher to reduce traffic.

Further, a capture can be performed in FortiGate to validate ARP and HA behavior. Refer to the sample capture screenshot.

Related article:

Troubleshooting Tip: FortiGate HA link-failed-signal and switching MAC address tables