4. Security Associations
This section defines Security Association management requirements for all IPv6 implementations and for those IPv4 implementations that implement AH, ESP, or both AH and ESP. The concept of a "Security Association" (SA) is fundamental to IPsec. Both AH and ESP make use of SAs, and a major function of IKE is the establishment and maintenance of SAs. All implementations of AH or ESP MUST support the concept of an SA as described below. The remainder of this section describes various aspects of SA management, defining required characteristics for SA policy management and SA management techniques.