What ports must be open for IPSec?
The USG9000 must have the following ports open for corresponding
Ports 500 and 4500 as the destination ports of UDP packets. If no NAT device
is deployed, use port 500. If any NAT device is deployed, use port 4500.
Port 51 for IP packets using the AH protocol and port 50 for IP packets using
the ESP protocol.