IPsec is a suite of protocols designed to provide security services for IP traffic. Major IPsec protocols include Authentication Header (AH), Encapsulating Security Payload (ESP), and Internet Key Exchange (IKE), as shown in Figure 4-1.
Figure 4-1. Major IPsec Protocols
It will be helpful to understand the major terms and protocols that are involved in IPsec negotiations. Those protocols and terminologies include the following:
Authentication Header: AH, defined in RFC 2402, uses IP number 51 and is a mechanism for providing integrity and authentication of IP packets. AH does not provide encryption.