What happens when a third router in an HSRP group is in the listen state?

When a third router in an HSRP (Hot Standby Router Protocol) group is in the listen state, it is essentially monitoring the situation within the group. In this state, the router does not take on an active or standby role; instead, it waits for a potential role change. If the active router fails or goes down, the router in the listen state is prepared to take over functions and support network connectivity.

This process allows redundancy and ensures that there is a standby router ready to respond if needed, which is a core feature of HSRP's design to provide fault tolerance and maintain network availability. The router in the listen state will regularly listen for HSRP hello packets from the active and standby routers to keep track of their status. If necessary, it can then transition to the active role to maintain network services.

This behavior ensures a smooth transition and contributes to overall network stability by minimizing disruption in case of a failure.