HSRP(Hot Standby Router Protocol)

  

Points to Remember .

-Need fault tolerance for L3 gateway
-Default Gateway assigned to customer is virtual IP address
-Both routers should provide service for default virtual gateway address.
-One of these routers(active)should respond for arp request from client.
-There will be fake mac-address for virtual default gateway.
-Here active router will have two mac address one for its own interface and next for default virtual gateway.
-Even if standby router changed to active , there won't be change in virtual gateway IP address and corresponding mac address.

Here is how preempt works. The router with the highest priority, becomes the active router, and will take over even if another router (with a lower priority) had been the active router.
The default is that preempt is not enabled. In this default state, if a router boots up, and sees that there is an active router, the new router (even if it has a higher priority) will simply let the current active router stay active.

  HSRP