This index is used as a secondary index to uniquely identify this row. A secondary index (this object) is meaningful to some but not all, LDP implementations. For example an LDP implementation which uses PPP would use this index to differentiate PPP sub-links. Another way to use this index is to give this the value of ifIndex. However, this is dependant on the implementation. When irrelevant, value = value = (2^32)-1 (all ones in all bits).