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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.
AH (Authentication Header) Protocol
The 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.
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.
To access the IPSec page:
1
Click VPN in the menu bar.
2
Then click the IPSec submenu.
Figure 39 shows an example of the menu and Table 31 describes the items you can
select.