In what scenario would an HSRP router send gratuitous ARP messages?

When an HSRP (Hot Standby Router Protocol) router transitions to an active role, it sends gratuitous ARP messages to inform the local devices on the network about its new primary IP address. This process helps to update the MAC address table of the devices connected to the same local area network. By sending a gratuitous ARP, the active router effectively announces itself in the network, allowing devices to learn the correct association between the IP address it serves and its MAC address. This is crucial for ensuring that network traffic is correctly routed to the active router, especially following an HSRP failover, where the active router may change depending on the network's state.

In contrast, while configuration changes can influence router behavior, gratuitous ARP is not a mandatory action for every configuration change. Scheduled intervals for ARP messages do not typically involve gratuitous ARP, which is a proactive measure. Lastly, gratuitous ARP is often associated with failover scenarios but is specifically triggered when a router becomes active rather than during the failover process itself. Hence, the context of the transition to an active role is key to understanding when gratuitous ARP messages are sent.