HSRP is a Cisco proprietary redundancy protocol, with this protocol one “virtual IP address “is assigned and always this address is used to go through the routers. At the backplane, the gateway interface’s IP address still exist. But it seems that only one interface exist and the IP address of this interface is virtual IP address
While using HSRP, there is a HSRP group and in this group there are gateway routers for specific roles.
1. Active router
2. Standby router
3. Listening routers
The Active Router is the router that is currently used as the gateway. The traffic goes through this router
The Standby router is the backup of Active Router. When the active router fails then this router is used as active.
Lastly the listening Router is other routers participating in this HSRP group
Active router is controlled by standby router with periodic hello packets by default every 3 seconds.
In case of a failure of active router, this mechanism provide switching to the back router.
The router roles are decided with priority values, the router that has the higher priority becomes active router. The default priority value is 100 in case of an equal priority values, ip address are used as the tie-break. The router with the highest ip address wins this election and become active router. And the other router that has the second high ip address become standby router.
HSRP progresses through some states. These states are mentioned below respectively.
1. Disable: not configured for HSRP or shutdown
2. Init: Stating state
3. Learn: waiting for hellos, to learn virtual address
4. Listen: Aware of virtual ip ,not elected standby or active
5. Speak: Participating in election, sending hellos
6. Standby: Acting as backup, monitors and send hellos
7. Active: Accepting and forwarding user traffic
Only in three stats, hello are sent, speak, standby, and active. As you know standby and active routers already send hellos each other. In the last one, in speak state, hellos are send to determine [d'tmn] the active and standby routers.
Thank you,
Arrow,Yang