HSRP V1 MAC address:

1- The first 24 bit are reserved to the vendor (Cisco in most cases)

2- The next 16 bit represent the HSRP Code or Id (07ac)

3- The last 8 bits represent the HSRP group number in Hexadecimal (0a for group 10 in the example below)

HSRP V2 MAC address:

 HSRP version 2 utilizes the MAC address range from 0000.0C9F.F000 through 0000.0C9F.FFFF (000 = Group 0, FFF = Group 4095).

Notes:

• The multicast address 224.0.0.2 is used to send HSRP hello messages. This address can conflict with Cisco Group Management Protocol (CGMP) leave processing.

• In HSRP version 1, millisecond timer values are not advertised or learned. HSRP version 2 advertises and learns millisecond timer values.