This object along with the ifIndex of a particular interface
uniquely identifies an HSRP group.
Group numbers 0,1 and 2 are the only valid group numbers
for TokenRing interfaces. For other media types, numbers
range from 0 to 255. Each interface has its own set of group
numbers. There's no relationship between the groups
configured on different interfaces. Using a group number
on one interface doesn't preclude using the same group
number on a different interface. For example, there can be
a group 1 on an Ethernet and a group 1 on Token Ring. More
details can be found from RFC 2281.