Hot Standby Router Protocol
Hot Standby Router Protocol (HSRP) is a Cisco proprietary redundancy protocol designed to provide high availability and failover capabilities for network routers. It allows multiple routers to work together in a group, with one router designated as the active router and the others as standby routers. In the event of a failure or disruption on the active router, one of the standby routers automatically takes over the traffic handling responsibilities.
- Redundancy and High Availability: HSRP provides redundancy and high availability for network routers by establishing a virtual IP address and virtual MAC address that can be used as the default gateway by devices on the network. This ensures that even if the active router fails, the standby router can seamlessly take over and continue routing traffic.
- Router Roles: In an HSRP group, routers are assigned different roles. The active router is responsible for forwarding traffic, while the standby routers monitor the health of the active router and are ready to take over if needed. Additional routers can be configured as standby routers to further enhance redundancy.
- Priority and Preemption: Each router in the HSRP group is assigned a priority value. The router with the highest priority becomes the active router. If multiple routers have the same priority, the one with the highest IP address is elected as the active router. Preemption allows a higher priority router to regain the active role when it becomes available again.
- Virtual IP and MAC Address: HSRP uses a virtual IP address and MAC address that are shared among the routers in the group. These addresses are used by devices on the network as the default gateway. The virtual IP and MAC addresses are associated with the active router, and if a standby router takes over, it assumes these addresses.
- Hello Messages and Tracking: HSRP routers exchange hello messages to monitor the health of each other. If a router stops receiving hello messages from the active router, it initiates the failover process. HSRP also supports interface tracking, where routers can monitor the status of certain interfaces and adjust their priorities accordingly.
- Load Balancing: HSRP supports load balancing by allowing multiple active routers in the same HSRP group, each handling traffic for different subnets. This enables better utilization of resources and improved network performance.
HSRP provides a reliable and seamless failover mechanism for network routers, ensuring uninterrupted network connectivity and minimizing downtime. It is widely used in enterprise networks and critical infrastructure where high availability and redundancy are essential requirements.