NAT-T with IKEv2 IPSEC

I think its just part of IKEv2 to do NAT Traversal in order for it to works if both ends source port must be fixed by a CGNAT if both ends are behind CGNAT and can't allow incoming.

So it be like this

USG60W <> ISP CGNAT <--> ISP CGNAT <> other USG

The here it the way NAT Traversal works both 500 and 4500 both ends nailed up

USG60W 10.0.0.2:4500 > 3.3.3.1:4500 > CGNAT 2.2.2.1:4500 > 3.3.3.1:4500 CGNAT 3.3.3.1 > 10.10.10.3:4500 other USG

which the othe USG does the same

other USG 10.10.10.3:4500 > 2.2.2.1:4500 > CGNAT 3.3.3.1:4500 > 2.2.2.1:4500 CGNAT 2.2.2.1 > 10.0.0.2:4500 USG60W

Then it Traversal

But if one end allows incoming you just need the other to be nailed up