Describes how HSRP provides first-hop routing redundancy for IP hosts by using active and standby routers that share a virtual IP address and MAC address.
HSRP is a first-hop redundancy protocol that
-
provides transparent failover for the first-hop IP router,
-
selects an active router to forward packets and a standby router to take over if the active router fails, and
-
presents a shared virtual IP address and MAC address as the default gateway for hosts.
HSRP router roles and failure detection
HSRP represents the default gateway as a virtual router. It uses priority values and hello messages to assign router roles and detect failures.
-
Active router: Receives and routes packets that are destined for the virtual MAC address.
-
Standby router: Takes control of the virtual IP and MAC addresses if the active router fails.
-
Hello messages: Multicast UDP messages that detect failures and maintain router roles.
-
Priority: Determines the active router. The interface with the highest priority becomes the active router.
Packets received on a routed port and destined for the HSRP virtual IP address terminate on the local router, whether that router is active or standby. This behavior applies to ping and Telnet traffic.
Packets received on a Layer 2 VLAN interface and destined for the HSRP virtual IP address terminate on the active router.