HSRP routers on a LAN communicate among themselves to designate two routers as active and standby. The active router sends periodic hello messages. The other HSRP routers listen for the hello messages. If the active router fails and the other HSRP routers stop receiving hello messages, the standby router takes over and becomes the active router. Because the new active router assumes both the phantom’s IP and MAC addresses, end nodes see no change. They continue to send packets to the phantom router’s MAC address, and the new active router delivers those packets.
