Specifications

CHAPTER 6

First Hop Redundancy

The Active router forwards traffic. The Standby is backup. The standby monitors periodic hellos (multicast to 224.0.0.2,

UDP port 1985) to detect a failure of the active router. On failure, the standby device starts answering messages sent to

the IP and MAC addresses of the virtual router.

The active router is chosen because it has the highest HSRP priority (default priority is 100). In case of a tie, the router

with the highest configured IP address wins the election. A new router with a higher priority does not cause an election

unless it is configured to preempt—that is, take over from a lower priority router. Configuring a router to preempt also

ensures that the highest priority router regains its active status if it goes down but then comes back online again.

Interface tracking reduces the active router’s priority if a specified circuit is down. This enables the standby router to take

over even though the active router is still up.

HSRP States

HSRP devices move between these states:

n Initial: HSRP is not running.

n Learn: The router does not know the virtual IP address and is waiting to hear from the active router.

n Listen: The router knows the IP and MAC of the virtual router, but it is not the active or standby router.

n Speak: Router sends periodic HSRP hellos and participates in the election of the active router.

n Standby: Router monitors hellos from active router and assumes responsibility if active router fails.

n Active: Router forwards packets on behalf of the virtual router.

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CCNP SWITCH 642-813 Quick Reference by Denise Donohue

Note:

The Learn state is not

actually seen in debugs

of HSRP.

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