Hot Standby Router Protocol (HSRP)

Hot Standby Router Protocol (HSRP) is a network protocol developed by Cisco to ensure high availability and reliability in IP networks. HSRP allows multiple routers to work together to present the illusion of a single virtual router to the hosts on a local network. In case the active router fails, one of the standby routers takes over as the active router, ensuring uninterrupted service.

HSRP functions by creating a virtual router consisting of an active router and one or more standby routers. The active router is the main router that handles traffic, while the standby routers monitor the active router's status. If the active router fails, the standby router with the highest priority becomes the new active router. This switch is seamless, with little to no interruption to network traffic.

HSRP uses a virtual IP address and virtual MAC address to represent the virtual router. These addresses are shared among the active and standby routers. Hosts on the local network are configured to use the virtual IP address as their default gateway. Since the virtual IP address does not change even when the active router changes, hosts do not need to be reconfigured if a router fails.

HSRP messages are exchanged between routers at regular intervals to ensure that each router's status is known. If a standby router detects that the active router is not responding, it will assume the role of the active router. This failover process happens quickly to minimize network downtime.

HSRP supports several advanced features, such as preemption, which allows a router with a higher priority to take over as the active router even if another router is currently active. Interface tracking is another feature that allows HSRP to monitor the status of other interfaces on the router, adjusting priorities accordingly to maintain optimal network performance.

Overall, HSRP is a critical protocol for network redundancy, ensuring that traffic continues to flow smoothly even in the event of a router failure. It is widely used in enterprise networks where uninterrupted network access is crucial.