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::gwWanPortLinkActive
snmptrap -v2c -c public <manager> '' 1.3.6.1.4.1.429.0.36

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]:62633->[192.168.30.10]:162]:
  DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (107723433) 12 days, 11:13:54.33
  SNMPv2-MIB::snmpTrapOID.0 = OID: USR-TRAP-MIB::gwWanPortLinkActive