How does the NAT-Traversal work in IPSEC on Cisco ASA?
Establishing IPSec Tunnels Between HUAWEI Firewalls and HUAWEI AR Routers in NAT Traversal Scenarios - HUAWEI USG Series Firewalls Interoperability Configuration Guide for VPN - Huawei
11. Remote Access and the Importance of Nat-T with IPSec - YouTube