Key Management; Encapsulation; Transport Mode; Tunnel Mode - ZyXEL Communications VANTAGE CNM 2.0 User Manual

Table 52 AH and ESP (continued)
AES
Advanced Encryption Standard data encryption uses a
secret key. This implementation of AES applies a 128-bit
key to 128-bit blocks of data. AES is faster than 3DES.
Select DES for minimal security and 3DES or AES for
maximum. Select NULL to set up a tunnel without
encryption.

11.1.8 Key Management

Key management allows you to determine whether to use IKE (ISAKMP) or manual key
configuration in order to set up a VPN.

11.1.9 Encapsulation

The two modes of operation for IPSec VPNs are Transport mode and Tunnel mode.

11.1.9.1 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.

11.1.9.2 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.
Chapter 11 Configuration > VPN
ESP
Vantage CNM 2.0 User's Guide
AH
Select MD5 for minimal security and SHA-
1 for maximum security.
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