This object identifies the index corresponding to the dataSource for this entry. For sorted values of variables belonging to the IF-MIB, EtherLike-MIB or TOKENRING-MIB, this value equals the ifIndex of the interface. For sorted values of variables belonging to the RMON-MIB, this value equals the interface corresponding to the data source, pointed to by the value of etherStatsDataSource. For sorted values of variables belonging to the BRIDGE-MIB, this value equals the interface corresponding to the bridge port, pointed to by the value of dot1dBasePortIfIndex.