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  Internet Protocol Concepts and Overview

IP Functions 1 2 Internet Protocol Version 4 (IP, IPv4)

IP-Related Protocols

In addition to our “old” and “new” versions of IP, there are several protocols that I call IP-related. They are not parts of IP proper, but protocols that add to or expand on the capabilities of IP functions for special circumstances. These are:

• IP Network Address Translation (IP NAT / NAT): This protocol provides IP address translation capabilities to allow private networks to be interfaced to public networks in a flexible manner. It allows public IP addresses to be shared and improves security by making it more difficult for hosts on the public network to gain unauthorized access to hosts. It is commonly called just “NAT” but it works on IP addresses so I think “IP NAT” is more clear.
  
  
• IP Security (IPSec): Defines a set of sub-protocols that provide a mechanism for secure transfer of data using IP. IPSec is rapidly growing in popularity as a security protocol to enable virtual private networks (VPNs).
  
  
• Mobile IP: A protocol that addresses some of the difficulties associated with using IP on computers that frequently move from one network to another. It provides a mechanism to allow data to be automatically routed to a mobile host (such as a notebook computer) without requiring the device's IP address to be constantly re-configured.

The remainder of the discussion of IP is divided into five sections corresponding to IPv4, IPv6, IP NAT, IPSec and Mobile IP.

IP Functions 1 2 Internet Protocol Version 4 (IP, IPv4)