When using FHRP, what happens if the primary device goes down?

When utilizing First Hop Redundancy Protocols (FHRP), such as HSRP, VRRP, or GLBP, the primary purpose is to ensure high availability of the default gateway for hosts in a network. If the primary device, which is the currently active gateway, goes down, the FHRP mechanism is designed to quickly and automatically promote the secondary device to an active state. This transition allows the secondary device to take over the responsibilities of routing traffic for the end hosts without the need for manual intervention.

This automatic failover minimizes downtime and ensures continuity of service, as the hosts can still communicate with outside networks. The secondary device's ability to seamlessly assume the role of the active device is a key feature of FHRP, enabling robust network resilience. The protocol uses predefined timers to detect failures and can respond effectively to changes in the network topology, ensuring that traffic can be rerouted with minimal impact on users.

While there may be scenarios where manual intervention is needed for certain configurations, the core functionality of FHRP is specifically tailored to provide automatic failover, which is why the promotion of the secondary device to active status is the desired behavior when the primary fails.