The network address which, when combined with the
corresponding value of the mask specified in
hwIpMcastRouteNextHopSourcePrefixLength, identifies the
sources for which this entry specifies a next-hop on an
outgoing interface.
This address object is only significant up to
hwIpMcastRouteNextHopSourcePrefixLength bits. The remainder
of the address bits are 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
source address applies only within the given zone. Zone
index zero is not valid in this table.