The address portion of the route used to find the upstream
or parent interface for this multicast forwarding entry.
This address object is only significant up to
hwIpMcastRouteGroupPrefixLength bits. The remainder of the
address bits are zero.
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.