ifConvertFmIfIndexIfIndex is the service ifIndex that serves as the index into ifConvertFmIfIndexTable, the reverse-lookup table that converts an ifIndex back into its board/netmod/port/channel service ID. Admins use this table when they already know an interface's ifIndex (e.g. from an interface-down trap) and need to find its physical location on the chassis. For example, looking up ifConvertFmIfIndexIfIndex=145 returns the associated board, netmod, port, and channel IDs identifying exactly which physical circuit that ifIndex represents.