Send this trap to an SNMP manager — replace <manager> with the IP or hostname of your monitoring server (SNMPv2c):

snmptrap -v2c -c public <manager> '' USR-TRAP-MIB::gwWanPortOutOfService
snmptrap -v2c -c public <manager> '' 1.3.6.1.4.1.429.0.35

Listen for incoming traps on the manager host (-f keeps it in the foreground, -Lo prints to stdout — useful for testing):

snmptrapd -f -Lo -c /dev/null authCommunity log public

Example snmptrapd log entry:

zoo11-linux.zoo [UDP: [192.168.30.111]:58643->[192.168.30.10]:162]:
  DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (122684691) 14 days, 4:47:26.91
  SNMPv2-MIB::snmpTrapOID.0 = OID: USR-TRAP-MIB::gwWanPortOutOfService