This reports which interface an active alarm is associated with, but uses a set of out-of-range sentinel values, 65001 for IDC-related alarms, 65003 and 65004 for drawer1 and drawer2, and 65000-plus-origin for anything with an origin number above 256, to represent alarms that aren't tied to any specific physical interface at all. Naively treating this as a normal ifIndex would misinterpret system-level alarms as interface faults, so alarm-handling scripts need explicit logic to recognize these reserved ranges. Seeing a value of 65003 in this field tells an admin the alarm is about drawer1 hardware, not about some phantom interface numbered 65003 in the ifTable.