Hot Standby Router Protocol is Cisco proprietary. One router is Active, one is Standby, and others are in Listen state.
The Active router handles all traffic to the virtual IP. The Standby monitors the Active via hello messages. If hellos stop (default seconds), the Standby waits the hold time (default seconds) and then takes over.
HSRP version uses multicast . Version uses . Version supports IPv and more group numbers. Always use version in new deployments.