The index value which uniquely identifies the local IPv6
interface through which this Adjacent Node should be reached.
The interface identified by a particular value of this
index is the same interface as identified by the same
value of wfIpv6IfIndex.
If this index is zero, this Adjacent Node is this router
itself, i.e. 'wfIpv6AdjNodeAddress' address is treated as
a router's own local address. IPv6 datagrams with such
a destination address are considered to be consumed by
this router itself. As an example, such an address can be
an IPv6 anycast address assigned to this router.