Chapter 24. Overview of the TCPIP Protocol Suite

Chapter 24. Overview of the TCP/IP Protocol Suite

SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE

TCP/IP and the OSI Reference Model 360

The Internet Protocol (IP) 364

The Address Resolution ProtocolResolving IP Addresses to Hardware Addresses 380

The Transmission Control Protocol (TCP) 386

The User Datagram Protocol (UDP) 395

Ports, Services, and Applications 397

The Internet Control Message Protocol (ICMP) 398

TCP/IP is the primary network protocol used on the Internet. Unlike many earlier network protocolssuch as ARCnet and DECnetTCP/IP was not developed by a single vendor as a proprietary solution. TCP/IP was created to provide a network link between computer hardware and software platforms from various vendors (such as IBM and Digital Equipment Corporation at the high end, as well as personal computers at the low end). By standardizing on a single set of protocols, each of which serves a specific function, TCP/IP can be used to create a network, no matter what underlying hardware is used. During the early years of TCP/IP, universities, businesses, and government organizations were able to exchange information on the ARPANETthe Internet's predecessorbecause TCP/IP could be implemented on just about any kind of computer. It is easy to implement TCP/IP on a wide variety of operating systems because TCP/IP was developed with a layered approach, which means that network functionality was compartmentalized into layers instead of the traditional approach of writing network drivers as single programs tied to specific hardware.

Using this layered approach means that a vendor need only write a low-level driver for their hardware to work with the upper layers of the TCP/IP code (which provides a standard interface). By freeing the development of the protocol(s) from the hands of particular manufacturers, TCP/IP has been developed to satisfy the needs of the many, instead of the needs of a single vendor's proprietary hardware. TCP/IP has evolved over time, using a process in which many individuals have had the opportunity to supply input into its development. The Request for Comments (RFCs) documents that you hear about all through this book are the documents that allow suggestions for protocol enhancements and new protocols to be reviewed by a diverse group of individuals who specialize in the particular topic at hand. Although many projects created by a committee turn out to be unwieldy, cumbersome works, this is not the case with TCP/IP. Instead, the RFC process allows for a great deal of input when creating standards, often resulting in a higher quality standard after scrutiny by experts in the field.

Note

Request for Comments documents can be useful when you are learning new technology. Over the years newer documents have superceded older standards documents as TCP/IP (and other related protocols used on the Internet) has matured. If you have difficulty understanding how a protocol works, or why it was developed the way it was, you can read the documents online at www.rfc-editor.org. This site contains all the RFC documentsboth new and those that have been replaced. Some of these documents are difficult to read at first but can prove valuable guides for readers who want to understand the minute details of any particular protocol.

In this chapter, we will look at all the major protocols that make up the TCP/IP suite and show how they work together. In addition to the protocols you will read about here, the TCP/IP suite includes some standard applications, such as FTP and Telnet. These are discussed in Chapter 25, "Basic TCP/IP Services and Applications." Finally, in Chapter 27, "Troubleshooting Tools for TCP/IP Networks," you will find useful information about programs that were written to help diagnose problems when this complex suite of protocols and applications doesn't appear to be working as it should.

To begin, it is important to understand the basic protocols on which the entire TCP/IP suite is built.