This read-only object gives the index value identifying the interface that a row of the sonusIpAddrTable applies to, matching the same interface identified by ifIndex in RFC 1573. It lets an admin cross-reference an IP address entry back to the corresponding interface row in the standard interfaces table for further diagnostics. For example, an admin troubleshooting why an IP address isn't responding would use this object's value to look up the matching row in ifTable and check its operational status.