ZyXEL P-661H-D1 User Guide - Page 232
Encapsulation, Table 62
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Chapter 16 VPN which is unchanged by a NAT device. The compatibility of AH and ESP with NAT in tunnel and transport modes is summarized in the following table. Table 62 VPN and NAT SECURITY PROTOCOL MODE AH Transport AH Tunnel ESP Transport ESP Tunnel NAT N N Y* Y Y* - This is supported in the ZyXEL Device if you enable NAT traversal. 16.6.4 Encapsulation The two modes of operation for IPSec VPNs are Transport mode and Tunnel mode. Figure 103 Transport and Tunnel Mode IPSec Encapsulation Tunnel Mode Tunnel mode encapsulates the entire IP packet to transmit it securely. A Tunnel mode is required for gateway services to provide access to internal systems. Tunnel mode is fundamentally an IP tunnel with authentication and encryption. This is the most common mode of operation. Tunnel mode is required for gateway to gateway and host to gateway communications. Tunnel mode communications have two sets of IP headers: • Outside header: The outside IP header contains the destination IP address of the VPN gateway. • Inside header: The inside IP header contains the destination IP address of the final system behind the VPN gateway. The security protocol appears after the outer IP header and before the inside IP header. 232 P-661HNU-Fx User's Guide