Route processors in the same or another chassis can share redundant gateway addresses on a VLAN by using the Hot Standby Router Protocol (HSRP).
Route processors sharing a common HSRP IP address must belong to the same HSRP group number.
The HSRP address appears on the network with a special virtual MAC address—00-00-0C-07-AC-XX, where XX is the HSRP group number (0 to 255). The hosts on the HSRP VLAN use this MAC address as the default gateway.
Although HSRP is enabled on an interface, each route processor still maintains its own unique IP and MAC addresses on the VLAN interface. These addresses are used by other routers for routing protocol traffic.
When an HSRP group is enabled, the highest-priority HSRP device ...