HSRP

Cisco's First-Hop Redundancy Solution

Hot Standby Router Protocol (HSRP) is Cisco's proprietary first-hop redundancy protocol, functionally similar to the open standard VRRPVirtual Router Redundancy Protocol. A protocol that assigns a virtual IP address to a group of routers, automatically failing over to a backup if the primary router goes down, providing gateway redundancy without manual reconfiguration.. HSRP allows a group of routers to present a single virtual IP and virtual MAC (0000.0c07.acXX) as the default GatewayA network device (typically a router) that serves as the access point from a local network to other networks. The default gateway is the first hop for traffic destined outside the local subnet. to hosts on a LAN segment. The Active router handles all traffic forwarded to the virtual IP; Standby routers monitor it and are ready to take over.

Active/Standby Election

HSRP routers elect an Active router based on configurable priority (default 100, range 1-255). The highest-priority router wins; ties are broken by highest real IP address. Routers send hello messages every 3 seconds by default; if the Active router fails to send hellos for the holdtime (default 10 seconds), the Standby router promotes itself to Active. Preemption must be explicitly configured — without it, a router recovering from failure does not reclaim the Active role even if it has higher priority.

HSRP Versions and Features

HSRPv1 uses multicast address 224.0.0.2 and supports up to 255 groups; HSRPv2 uses 224.0.0.102 and extends to 4096 groups, adding millisecond timer support and IPv6Internet Protocol version 6. The successor to IPv4 using 128-bit addresses (e.g., 2001:0db8::1), providing a virtually unlimited address space of 3.4 x 10^38 addresses. Designed to solve IPv4 address exhaustion. capabilities. Interface tracking allows HSRP priority to decrease automatically when an upstream interface goes down, triggering an Active failover even though the HSRP interface itself is still up — a critical feature for detecting upstream failures the hosts cannot see. HSRP is widely deployed in enterprise access and distribution layers.