ipv6 Udp If Index
An index object used to disambiguate conceptual rows in the table, since the ipv6UdpLocalAddress/ipv6UdpLocalPort pair may not be unique. This object identifies the local interface that is associated with ipv6UdpLocalAddress for this UDP listener. 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 ipv6UdpLocalAddress 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 this UDP endpoint.
Back to IPV6-UDP-MIB MIB page.