ZyXEL Communications VPN Series Handbook page 196

www.zyxel.com
please check ZyWALL/USG and WatchGuard Phase 2 Settings. Both ZyWALL/USG
and WatchGuard must use the same Protocol, Encapsulation, Encryption,
Authentication method and PFS to establish the IKE SA.
MONITOR > Log
Make sure the both ZyWALL/USG and WatchGuard security policies allow IPSec
VPN traffic. IKE uses UDP port 500, AH uses IP protocol 51, and ESP uses IP protocol
50.
Default NAT traversal is enable on ZyWALL/USG, please make sure the remote
IPSec device must also have NAT traversal enabled.
196/810