Transport mode ESP with authentication is not compatible with NAT, although NAT traversal
provides a way to use Transport mode ESP when there is a NAT router between the IPSec endpoints
(see section 16.7 for details).
Introduction to IPSec
Table 15-1 VPN and NAT
SECURITY PROTOCOL
AH
AH
ESP
ESP
Prestige 662HW Series User's Guide
MODE
NAT
Transport
N
Tunnel
N
Transport
N
Tunnel
Y
15-5