20:11:29.900209 bge0 @200:65 b 12.1.83.251,4500 -> 172.20.1.98,54224 PR udp len 20 176 IN bad NAT
Please try again after disabling hardware checksumming using the following command on /exec.php for each interface (bge0 etc.):
ifconfig bge0 -rxcsum -txcsum
(this change will be lost on reboot)
I suspect that the problems with IPsec NAT-T passthrough (i.e. port 4500) have something to do with the way the built-in NAT-T support in FreeBSD works in conjunction with hardware checksumming on the NICs.