HSRP is a Cisco proprietary First Hop Redundancy Protocol in cases of Router# failures which causes problems in routing. The default hello interface is 3 seconds, and the default hold time is 10 seconds.
The command standby {group-id} ip {virtual-ip-addr} run in Interface Configuration Mode will create a virtual router with the assigned virtual IP Address#. The IP address could be extracted using Variable-Length Subnet Masking (VLSM). Any other router interface in the network with the same HSRP group ID will be viewed logically as a virtual router. Within virtual router there consists of two entities: active router and standby routers. There could be only one active router in a group. Its responsibility will be to forward traffic on behalf of the virtual router to the destination unless it fails. If the active router fails, standby routers can come into play.
The election of the active router will be determined on the standby routers’ priority, which can be set with standby {group-id} priority {value}. The highest priority standby router will be elected as the active router. If the priorities are the same among the routers, then the one with the highest IP address will be elected. However, if there is already an active router in acting, standby routers will not replace it even with higher priority and/or higher IP address. These all things will be reset once one of the router, especially the active router, reboots. To let the router regaining its previous position, enable it by standy {group-id} preempt in Interface Configuration Mode.
Note: The priority of a router is defaulted to 100.
After the set-up of HSRP, the clients should set their gateway to the corresponding virtual router’s IP address, i.e., virtual IP address in order to get the effect.