What is HSRP (Hot Standby Router Protocol)?

Hot Standby Router Protocol (HSRP) is a Cisco proprietary redundancy protocol that provides high availability for routers, particularly in a network environment where continuous access to the internet or critical resources is essential. HSRP allows for the automatic failover of a router in the event of a failure, ensuring that network traffic is seamlessly redirected to a backup or standby router.

Here's how HSRP works:

1. Active Router: One router is designated as the active router, and it is responsible for forwarding the traffic on the network. This router assumes the virtual IP address associated with the HSRP group.
2. Standby Router: Another router is designated as the standby router. It monitors the status of the active router and takes over if the active router fails. The standby router assumes the virtual IP address when it becomes active.
3. Virtual IP Address: HSRP uses a virtual IP address that floats between the active and standby routers. This virtual IP address is what clients use as their default gateway.
4. Hello Packets: HSRP routers exchange "hello" packets at regular intervals to detect the health of each other. If the active router fails to send hello packets within a specified timeframe, the standby router assumes the active role.

By using HSRP, network administrators can enhance the reliability and fault tolerance of their networks. It is commonly employed in scenarios where a single point of failure is undesirable, such as in branch offices, data centers, or other critical network locations.