What message type is exchanged between FHRP routers to maintain their state?

The correct answer is "Hello messages" because in the context of First Hop Redundancy Protocols (FHRP) such as HSRP (Hot Standby Router Protocol), VRRP (Virtual Router Redundancy Protocol), and GLBP (Gateway Load Balancing Protocol), Hello messages are essential for routers to communicate their current state and maintain an active backup relationship.

Hello messages are periodically sent by the primary and backup routers to inform each other that they are alive and functioning. This regular exchange helps to ensure that both routers are synchronized in their roles as active or standby, allowing for seamless failover in case the active router goes down. If Hello messages are not received within a predefined interval, the backup router can assume that the active router has failed and take over as the new active router.

The other message types do not encompass this specific function: Control messages can refer to many types of communication regarding network management but are not specific to the state maintenance of FHRP routers. Configuration messages are typically used to set up elements of networking devices but are not exchanged for state maintenance tasks. Status messages might convey some information about device states but do not specifically indicate the active role or failure responses necessary for FHRP operations.