Packet Guide to Core Network Protocols

Chapter 3. Internet Protocol

“During my service in the United States Congress, I took the initiative in creating the Internet.”

— Al Gore

“He [Al Gore] is indeed due some thanks and consideration for his early contributions.”

— Vint Cerf

As stated in Chapter 2, the language of the Internet and of the networks connected to the Internet is TCP/IP. This chapter examines the later part of this protocol pair. The Internet Protocol (IP) exists at Layer 3, regardless of which model you are using as a reference. It is often referred to as a “best effort” protocol, which simply means that IP provides very little in the way of connection or error control. Communication networks rely on upper-layer protocols such as TCP and the associated applications to handle these issues. However, all applications and processes running on the network have one thing in common—they all use IP. So, it is critical that we understand the operation of this ubiquitous protocol. This chapter takes an in-depth look at the protocol fields and their uses, operations, and the addressing used for networks today.

Protocol Description

IP has been around for more than three decades. Perhaps the easiest and best place to start is with RFC 791, titled “Internet Protocol DARPA Internet Protocol Specification.” This RFC was written in 1981, and the following quote gives some indication of its roots and age:

This document is based on six earlier editions of the ARPA Internet Protocol Specification, and the present text draws heavily ...