ZyXEL Communications P-2602HW(L) Series - Manual (Page 221)

P-2602H(W)(L)-DxA Series User’s Guide
Chapter 17 VPN Screens 221
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H A P T E R
17
VPN Screens
This chapter introduces the VPN screens. See Chapter 24 on page 295 for information on
viewing logs and the appendix for IPSec log descriptions.
17.1 VPN/IPSec Overview
Use the screens documented in this chapter to configure rules for VPN connections and
manage VPN connections.
17.2 IPSec Algorithms
The ESP and AH protocols are necessary to create a Security Association (SA), the
foundation of an IPSec VPN. An SA is built from the authentication provided by the AH and
ESP protocols. The primary function of key management is to establish and maintain the SA
between systems. Once the SA is established, the transport of data may commence.
17.2.1 AH (Authentication Header) Protocol
AH protocol (RFC 2402) was designed for integrity, authentication, sequence integrity (replay
resistance), and non-repudiation but not for confidentiality, for which the ESP was designed.
In applications where confidentiality is not required or not sanctioned by government
encryption restrictions, an AH can be employed to ensure integrity. This type of
implementation does not protect the information from dissemination but will allow for
verification of the integrity of the information and authentication of the originator.
17.2.2 ESP (Encapsulating Security Payload) Protocol
The ESP protocol (RFC 2406) provides encryption as well as the services offered by AH. ESP
authenticating properties are limited compared to the AH due to the non-inclusion of the IP
header information during the authentication process. However, ESP is sufficient if only the
upper layer protocols need to be authenticated.
An added feature of the ESP is payload padding, which further protects communications by
concealing the size of the packet being transmitted.