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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  IP Security (IPSec) Protocols

IPSec Overview, History and Standards 1 2 3 IPSec Architectures and Implementation Methods

IPSec Support Components

AH and ESP are commonly called “protocols”, though this is another case where the validity of this term is debatable. They are not really distinct protocols but are implemented as headers that are inserted into IP datagrams, as we will see. They thus do the “grunt work” of IPSec, and can be used together to provide both authentication and privacy. However, they cannot operate on their own. For them to function properly they need the support of several other protocols and services. The most important of these include:

• Encryption/Hashing Algorithms: AH and ESP are generic and do not specify the exact mechanism used for encryption. This gives them the flexibility to work with a variety of such algorithms, and to negotiate which is used as needed. Two common ones used with IPSec are Message Digest 5 (MD5) and Secure Hash Algorithm 1 (SHA-1). These are also called hashing algorithms because they work by computing a formula called a hash based on input data and a key.
  
  
• Security Policies and Associations, and Management Methods: Since IPSec provides flexibility in letting different devices decide how they want to implement security, some means is required to keep track of the security relationships between devices. This is done in IPSec using constructs called security policies and security associations, and by providing ways to exchange security association information (see below).
  
  
• Key Exchange Framework and Mechanism: For two devices to exchange encrypted information they need to be able to share keys for unlocking the encryption. They also need a way to exchange security association information. In IPSec, a protocol called the Internet Key Exchange (IKE) provides these capabilities.

Well, that's at least a start at providing a framework for understanding what IPSec is all about and how the pieces fit together. We’ll examine these components and protocols in more detail as we proceed through this section.

IPSec Overview, History and Standards 1 2 3 IPSec Architectures and Implementation Methods