ZyXEL P-2602HW-D3A User Guide - Page 218

IPSec and NAT

Page 218 highlights

P-2602H(W)(L)-DxA Series User's Guide Figure 119 Transport and Tunnel Mode IPSec Encapsulation 16.3.1 Transport Mode Transport mode is used to protect upper layer protocols and only affects the data in the IP packet. In Transport mode, the IP packet contains the security protocol (AH or ESP) located after the original IP header and options, but before any upper layer protocols contained in the packet (such as TCP and UDP). With ESP, protection is applied only to the upper layer protocols contained in the packet. The IP header information and options are not used in the authentication process. Therefore, the originating IP address cannot be verified for integrity against the data. With the use of AH as the security protocol, protection is extended forward into the IP header to verify the integrity of the entire packet by use of portions of the original IP header in the hashing process. 16.3.2 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. 16.4 IPSec and NAT Read this section if you are running IPSec on a host computer behind the ZyXEL Device. 218 Chapter 16 Introduction to IPSec

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P-2602H(W)(L)-DxA Series User’s Guide
218
Chapter 16 Introduction to IPSec
Figure 119
Transport and Tunnel Mode IPSec Encapsulation
16.3.1
Transport Mode
Transport
mode is used to protect upper layer protocols and only affects the data in the IP
packet. In
Transport
mode, the IP packet contains the security protocol (
AH
or
ESP
) located
after the original IP header and options, but before any upper layer protocols contained in the
packet (such as TCP and UDP).
With
ESP,
protection is applied only to the upper layer protocols contained in the packet. The
IP header information and options are not used in the authentication process. Therefore, the
originating IP address cannot be verified for integrity against the data.
With the use of
AH
as the security protocol, protection is extended forward into the IP header
to verify the integrity of the entire packet by use of portions of the original IP header in the
hashing process.
16.3.2
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.
16.4
IPSec and NAT
Read this section if you are running IPSec on a host computer behind the ZyXEL Device.