TCP/IP Analysis and Troubleshooting Toolkit

CHAPTER 3

Inside the Internet Protocol

Now that Part I of the book has discussed the building blocks of communication (the OSI model) and some techniques on how to analyze those communications, it's time to start discussing what makes communications happen—the protocols. This next part of the book discusses the core TCP/IP protocols that allow all other upper-layer protocols to operate. The approach is once again layer by layer, starting with Internet Protocol (IP) in this chapter and moving on to the most complex core protocol, Transmission Control Protocol (TCP). It is important to understand how the bottom layered protocols such as IP work before you begin trying to understand the higher-layer protocols. Since each of the higher-layer protocols (such as UDP and TCP) use the services of the lower-layer protocols (such as IP), it's important to understand the impact of each layer's responsibility to the entire communications process. Such understanding is critical in troubleshooting situations. I begin this chapter with a review of Layer 2 communications and how the limitations of Layer 2 create a need for Layer 3 protocols. Then, instead of generic layer descriptions, I begin the discussion of the actual functions of the protocols at each layer, starting in this chapter with IP and other supporting protocols at the network layer.

Reviewing Layer 2 Communications

The next sections provide a quick review of what Part I revealed about the functions of Layer 2.

Multiplexing

Layer ...