Hi Rajesh,

SLB switch running the HSRP detects a failure by sending and receiving multicast User Datagram Protocol (UDP) "hello" packets. When the SLB switch running HSRP detects that the designated active SLB switch has failed, the selected backup SLB switch assumes control of the HSRP group MAC and IP addresses.

Just go thro. this document for better understanding,

http://www.cisco.com/en/US/docs/switches/lan/catalyst4840g/12.0_10_w5_18/configuration/guide/4840red.html#wp1020583

Rate if it does,

Rgs.