Port number used by the USG for NAT traversal

The USG firewalls use open port numbers for IPSec NAT traversal.
UDP packets with destination port set to 500 or 4500. If no NAT device exists, the port number is set to 500; if the NAT device exists, the port number is set to 4500.
IP packets using the AH (port number set to 51) or ESP (port number set to 50).

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