6 CHAPTER Securing TCP/IP After reading this chapter, you will be able to: ■ Explain the role that the Transmission Control Protocol (TCP) and the Internet Protocol (IP) play in computer networking ■ Understand how security concepts integrate into the OSI network- ing models ■ Identify the major components of the TCP/IP protocol suite and explain how each is used in networking ■ Decipher the contents of a TCP/IP packet and describe the types of modifications involved in malformed packet attacks ■ Describe the enhancements provided by adding IPSec security to a network ■ Identify the various security protocols used to enhance Web commu- nications and choose the protocol appropriate for a given situation chapple06 10/12/04 9:21 AM Page 135
136 CHAPTER 6 Securing TCP/IP The vast majority of computer networks, including the Internet itself, are dependent upon a set of protocols known as the TCP/IP suite. The two core components of this suite, the Transmission Control Protocol (TCP) and the Internet Protocol (IP), control the formatting and routing of data as it flows from point to point across the network.Although a large number of other net- work protocols are in use today (such as Novell’s Internetwork Packet Exchange/Sequenced Packet Exchange [IPX/SPX] and Apple’s AppleTalk),the discussion in this book is limited to these popular protocols because they are the“language of the Internet”and the source of many security vulnerabilities. 6.1 Introduction to Transmission Control Protocol/ Internet Protocol (TCP/IP) Although the TCP/IP suite has been modified and enhanced over the years, the core set of protocols date back to the earliest days of the Internet, when it was a private network interconnecting several large U.S. government research sites. These protocols completely describe the ways that devices communicate on TCP/IP networks, ranging all the way from the way individual chunks of data (known as packets ) are formatted to the details of how those packets are routed through vari- ous networks to their final destinations. In this section, we introduce the basic concepts behind the TCP/IP suite. You’ll first learn about the four protocols that form the basic building blocks of TCP/IP. Next, you’ll learn about how the Open Systems Inter- connection (OSI) reference model governs the design of TCP/IP and other networking protocols. Finally, you’ll learn how to examine the “guts” of a packet and actually interpret those electrical impulses as they transit a network. 6.1.1 TCP/IP Protocols Four main protocols form the core of TCP/IP: the Internet Protocol (IP), the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Control Message Protocol (ICMP). These proto- cols are essential components that must be supported by every device that communicates on a TCP/IP network. Each serves a distinct purpose and is worthy of further discussion.
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