A linkDown trap signifies that the SNMP entity, acting in an agent role, has detected that the ifOperStatus object for one of its communication links is about to enter the down state from some other state (but not from the notPresent state). This other state is indicated by the included value of ifOperStatus.
1.3.6.1.6.3.1.1.5.3
Trap : linkDown
Objects : { ifIndex, ifAdminStatus, ifOperStatus }
OID : "1.3.6.1.6.3.1.1.5.3"
object : ifIndex type : INTEGER
object : ifAdminStatus type : INTEGER
object : ifOperStatus type : INTEGER