This read-only object carries the same value as the standard ifIndex for the clock port, giving it a second, index-based identity used to uniquely identify the port within the clock table. An administrator uses it to cross-reference this timing-specific row with the generic interface table, where counters and descriptions for the same physical port also live. For example, looking up ifDescr for the ifIndex value returned here would reveal the human-readable name of the clock port.