An index object used to disambiguate conceptual rows in
the table, since the connection 4-tuple may not be unique.
If the connection's remote address (ipv6TcpConnRemAddress)
is a link-local address and the connection's local address
(ipv6TcpConnLocalAddress) is not a link-local address, this
object identifies a local interface on the same link as
the connection's remote link-local address.
Otherwise, this object identifies the local interface that
is associated with the ipv6TcpConnLocalAddress for this
TCP connection. If such a local interface cannot be
determined, this object should take on the value 0.
(A possible example of this would be if the value of
ipv6TcpConnLocalAddress is ::0.)
The interface identified by a particular non-0 value of this
index is the same interface as identified by the same value
of ipv6IfIndex.
The value of this object must remain constant during the life
of the TCP connection.
This object is obsoleted by the zone identifier in
an InetAddressIPv6z address in either
TCP-MIB::tcpConnectionLocalAddress or
TCP-MIB::tcpConnectionRemAddress.