The IP multicast group address which, when combined with the corresponding value specified in ipMcastRouteGroupPrefixLength, identifies the groups for which this entry contains multicast routing information. This address object is only significant up to ipMcastRouteGroupPrefixLength bits. The remaining address bits are set to zero. This is especially important for this index field, which is part of the index of this entry. Any non-zero bits would signify an entirely different entry. For addresses of type ipv4z or ipv6z, the appended zone index is significant even though it lies beyond the prefix length. The use of these address types indicate that this forwarding state applies only within the given zone. Zone index zero is not valid in this table.