Hot Standby Router Protocol - Definition

Hot Standby Router Protocol (HSRP) is a Cisco proprietary routing protocol for fault-tolerant routing, and has been described in detail in RFC 2281.

The protocol establishes a framework between network routers in order to achieve failover routes if the primary route should become inaccessible, in close association with a rapid-converging routing protocol like EIGRP or OSPF. By multicasting packets, HSRP sends its hello messages to the multicast address 224.0.0.2 (all routers) using UDP port 1985, to other HSRP-enabled routers, defining priority between the routers, the primary router with the highest configured priority will act as a virtual router with its own IP and MAC address, which the hosts on the local segment will be configured to use as a gateway to the destination in question. If the primary router should fail, or the link to the destination drop, the router with the next-highest priority would take over communications through alternative routes within seconds, without major interruption to network connectivity.

External link

• Cisco: HSRP Features (http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a91.shtml)
• Cisco: Using HSRP for Fault-Tolerant IP Routing (http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/cs009.htm)