ZyXEL P-660HNU-F1 User Guide - Page 215

Encapsulation, Tunnel Mode

Page 215 highlights

Chapter 16 VPN • Set the NAT router to forward UDP port 500 to IPSec router A. Finally, NAT is compatible with ESP in tunnel mode because integrity checks are performed over the combination of the "original header plus original payload," 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 67 VPN and NAT SECURITY PROTOCOL AH AH ESP ESP MODE Transport Tunnel Transport 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 112 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. ADSL Series User's Guide 215

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Chapter 16 VPN
ADSL Series User’s Guide
215
Set the NAT router to forward UDP port 500 to IPSec router
A
.
Finally, NAT is compatible with ESP in tunnel mode because integrity checks are performed over the
combination of the "original header plus original payload," 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.
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 112
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.
Table 67
VPN and NAT
SECURITY PROTOCOL
MODE
NAT
AH
Transport
N
AH
Tunnel
N
ESP
Transport
Y*
ESP
Tunnel
Y