TCP / IP For Dummies E-Book

Candace Leiden

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 601

Veröffentlichungsjahr: 2009

Beschreibung

Packed with the latest information on TCP/IP standards and protocols TCP/IP is a hot topic, because it's the glue that holds the Internet and the Web together, and network administrators need to stay on top of the latest developments. TCP/IP For Dummies, 6th Edition, is both an introduction to the basics for beginners as well as the perfect go-to resource for TCP/IP veterans. The book includes the latest on Web protocols and new hardware, plus very timely information on how TCP/IP secures connectivity for blogging, vlogging, photoblogging, and social networking. Step-by-step instructions show you how to install and set up TCP/IP on clients and servers; build security with encryption, authentication, digital certificates, and signatures; handle new voice and mobile technologies, and much more. * Transmission Control Protocol / Internet Protocol (TCP/IP) is the de facto standard transmission medium worldwide for computer-to-computer communications; intranets, private internets, and the Internet are all built on TCP/IP * The book shows you how to install and configure TCP/IP and its applications on clients and servers; explains intranets, extranets, and virtual private networks (VPNs); provides step-by-step information on building and enforcing security; and covers all the newest protocols * You'll learn how to use encryption, authentication, digital certificates, and signatures to set up a secure Internet credit card transaction Find practical security tips, a Quick Start Security Guide, and still more in this practical guide.

Leseprobe

TCP/IP For Dummies®

TCP/IP For Dummies®, 6th Edition

by Candace Leiden and Marshall Wilensky

Foreword by Scott Bradner

University Technology Security Officer, Harvard University

TCP/IP For Dummies®, 6th Edition

Published byWiley Publishing, Inc.111 River St.Hoboken, NJ 07030-5774www.wiley.com

Copyright © 2009 by Wiley Publishing, Inc., Indianapolis, Indiana

Published simultaneously in Canada

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About the Author

Forced to learn about computers because she was afraid of slide rules, Candace Leiden has worked as a software developer, system administrator, and database designer and administrator. Formerly the president of Cardinal Consulting, Inc., Candace is now a systems and database performance consultant and instructional design consultant for international courseware in those areas. Her customers have included Cardinal Consulting, Compaq Computer, Digital Equipment Corporation, the United Nations, several major pharmaceutical corporations, Oracle Corporation, and Hewlett-Packard. Candace is an internationally recognized speaker on relational databases and the Linux and Unix operating systems. Candace is also the author of Linux Bible (Wiley Publishing). Candace met Marshall Wilensky in 1981, when they worked at the same company. She taught him everything he knows.

Marshall Wilensky has been wrangling computers and networks for more than 30 years (and still has fewer wrinkles than Candace and less gray hair). In corporate life, he has had the privilege of working for companies ranging from 25 people (who are 25 years old) to more than 300,000 worldwide. He has been a consultant, a programmer, a system administrator, and a network manager for large multivendor and multiprotocol networks, including those at the Harvard University Graduate School of Business Administration.

Marshall met Candace Leiden in 1981 when they worked at the same company. He taught her everything she knows. They are also, most importantly, married (to each other). Candace and Marshall are both members-at-large of ICANN (Internet Corporation for Assigned Names and Numbers).

Dedication

Candace dedicates this book to Marshall Wilensky (no one knows the meaning of the phrase “in sickness and in health” better than Marshall) and to Emily Duncan, who is wise beyond her years. Even though she has been through some tough times, Emily rules!

Marshall dedicates this edition of the book to his late parents, Leo and Estelle Wilensky, and to Roxcy Platte and the people who help him with the toughest subject he has ever tackled.

In memory of:

Helen Louise Duncan

Christine Evans Staley

They are missed every day.

Author’s Acknowledgments

Thanks to everyone at Wiley who worked on this book. We continue to be surprised at how many people it takes to create a book. We’d like to thank the team at Wiley for putting up with us. Thanks also go to Katie Mohr, for her patience and diplomacy. So many people worked hard to turn our manuscript into a real book. Thanks also to our project editor, Kim Darosett, who never once had a discouraging word. When we finish a manuscript, Kim still has a lot of hard work to do. We’re grateful to Kim, Rebecca Whitney, Jen Riggs, and Barry Childs-Helton for their hard work. Their edits make this a better book in many ways. We appreciate the work the Composition Services department did in drawing tidy figures from our rough, hand-drawn sketches and in making our screen shots and text files look nice.

Finally, thank you to Cynthia Woods, a gifted and inspiring musician, who allowed us to use her beautiful Web page as one of our examples.

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Foreword

For both good and ill, modern society around the world has been transformed by the Internet. But the Internet was not the first data communications network, not by a long shot. So what was it about the Internet that enabled the revolution? In a very basic way, it was the use of TCP/IP. TCP/IP enabled the Internet to be the first data network where the use could be driven by the users and not controlled by the carriers. TCP/IP is an end-to-end protocol. The network is there to carry the bits from any device at the edge of the network to any other device. This stands in stark contrast to X.25, frame relay, ATM, and other carrier-managed data networks, where the carrier determined who you could talk to, and in an even starker contrast to the phone network, where the carrier determined what you could do.

This end-to-end architecture has resulted in an amazing proliferation of applications because the network does not get in the way of individual entrepreneurs developing the next great thing and running it over the Internet. It also did not get in the way of millions of people putting up their own Web pages, or, with somewhat more controversy, swapping music and movie files. Even if you take into account the Internet boom and subsequent bust, the Internet, and TCP/IP, are here to stay. And, while here, they will continue to radically change the way we interact with employers, service providers, each other, and the world at large.

You can easily go through life without having to understand how this Internet thing works because it will continue to work even if you do not understand it. I do not have any meaningful understanding of the Theory of Relativity yet make use of its implications every day.

TCP/IP For Dummies, 6th Edition, is for those of you who aren’t just curious about how things work, but who want to actually understand what’s behind the curtain. (Hint: It’s not the Wizard of Oz.)

— Scott BradnerUniversity Technology Security Officer, Harvard University

Introduction

TCP/IP is the glue that holds together the Internet and the World Wide Web. To be well connected (network-wise, that is), sooner or later you have to become familiar with TCP/IP applications and services. If you want to understand what TCP/IP is, what it’s for, why you need it, and what to do with it, and you just don’t know where to start — this book is for you.

If you’re on a network, whether you know it or not, odds are, you’re working with TCP/IP and its many pieces and parts. We help you understand how it all fits together. We also give you plenty of hands-on tips so that you can get all those pieces and parts set up and running.

We take the mystery out of TCP/IP by giving you down-to-earth explanations for all the buzzwords and technical jargon that TCP/IP loves.

This isn’t a formal tutorial; skip around and taste TCP/IP in little bites. If you need to impress your boss and colleagues with buzzwords, you can find out just enough to toss them around intelligently with the technocrats at meetings and parties. Or, you can go further and discover how to set up and use the most important features and tools. If you want the full TCP/IP banquet, you can explore the technical tasks that take place behind the scenes to make the Internet and the Web work. It’s right here in your hands.

About This Book

We hope you find TCP/IP For Dummies, 6th Edition, to be a fun and fast way to dive into the guts of the Internet. The book is both an introduction to the basics and a reference to help you work with Internet applications and tools on all kinds of connected computers. We added and updated the latest Internetworking protocols and servers — with examples from Microsoft Windows Server 2008, Windows 7, Windows Vista, Windows XP, Linux, Unix, and Mac OS X. Here are just a few of the subjects we describe:

Uncover the relationships among TCP/IP, the Net, and the Web.

Get up and running and keep running on the Internet, whether you have a small network or a big enterprise network and whether it’s wired or wireless.

Install and configure TCP/IP client and server applications and services.

Phone home without the phone or the bill, thanks to VoIP.

Build and enforce security everywhere on your network.

Get in on all the newest Internet security protocols and trends.

Boldly go to the next generation: IPv6.

This book is loaded with information. But don’t try to read it from cover to cover in one sitting — you may hurt yourself. If your head explodes and bits and bytes go flying, please don’t blame us.

Conventions Used in This Book

All commands that you need to enter yourself appear either in bold, like this, or on a separate line, like this:

COMMAND to type

To enter this command, you type COMMAND to type exactly as you see it here and then press Enter.

When you type commands, be careful to use the same upper- and lowercase letters that we show you. (Some computer systems are fussy about this issue.)

When we want you to move through a series of menus or buttons, we say “Click” once and then point to the next place with a command arrow (⇒).

Whenever we show you something that’s displayed onscreen (such as an error message or a response to your input), it looks like this:

A TCP/IP message on your screen

Foolish Assumptions

In writing this book, we tried not to make too many assumptions about you. We figure that you’ve done a little Web browsing and e-mailing. Our only assumption is that you’re not really a dummy — you’re just trying something new. Good for you!

How This Book Is Organized

This book contains five parts, each of which contains several chapters. We don’t expect you to read the whole book from cover to cover, but please feel free to do so. Instead, you can glance at the table of contents for the topic you’re interested in and go from there. The layout of the book is easy to follow. Here’s a quick look at what you can find in each major part.

Part I: TCP/IP from Names to Addresses

Part I starts at the beginning with the buzzwords and how TCP/IP and the Internet are joined at the hip. You also find out that, contrary to its name, TCP/IP is so much more than just two protocols. We give you a quick look at the most important protocols, and you get to see all the lingo that should take you far through this century.

You’ll find that as much as people like names, computers like numbers even more. After you get some of the buzzwords under your belt, the chapters in Part I explain what an Internet protocol (IP) address is, how to build one, how to use it, and how to be frugal and save enough Internet addresses for someone else. We clue you in on different ways to make IP addresses go further. No worries — the Internet won’t get full.

Part II: Getting Connected

After you know how IP addresses are constructed, we move on to setting up your TCP/IP network, both wired and wireless, to connect to the world (the Internet). In this part of the book, we show you how hardware and software work together to make a network. We discuss just the minimum hardware you need to understand.

Then we throw in IPv6, which puts you ahead of most people in understanding the next generation of Internet addresses. If you’re not ready to go where no one (well, hardly anyone) has gone before, don’t worry — you can skip Chapter 9 entirely.

Part III: Configuring Clients and Servers: Web, E-Mail, and Chat

TCP/IP is a big set of protocols, services, and applications. Whether you’re aware of it or not, you use TCP/IP applications and services to do everything from reading news to exchanging e-mail and online conversations with your friends to copying good stuff like games, technical articles, and even TCP/IP itself. This section explains how these applications and services work behind the scenes with client/server technology. The numerous hands-on sections help you configure popular applications and services for both clients and servers.

Security is one of the stars of Part III. Hackers love to try to break into your Web, e-mail, and chat applications, and we love to show you how to thwart their every move. We throw in a quick-start security guide to get you going. If you’re interested in online shopping or banking, we walk you through a secure Internet credit card transaction.

Part IV: Even More TCP/IP Applications and Services

“How could there possibly be more?” you might ask. Well, we told you that TCP/IP consists of much more than just a couple of protocols — for example, there’s Mobile IP, for when you take your laptop to your favorite café rather than to your office. If you have a smartphone or organizer, such as a Palm or BlackBerry, you need to know this stuff. But wait! There’s more. How about saving big bucks on phone calls? With or without a phone? Voice over Internet Protocol, or just VoIP, lets you make calls, even international ones, for free. Finally, Part IV covers remote access applications, from sharing files to working on someone else’s computer when you’re 5,000 miles away.

Part V: Network Troubleshooting and Security

Part V delves into some advanced topics. If you’re a system or network administrator, you may need to know more than just the basics about network hardware. We hope that after you install and configure TCP/IP and your network applications, nothing ever goes wrong for you, but stuff happens. Part V steps you through a basic troubleshooting procedure so that you can figure out what went wrong and where. Then you can fix it.

The rest of Part V is devoted to security. You find practical security tips, and you can delve deeper, to see how to use encryption, authentication, digital certificates, and signatures. You get hands-on advice for setting up a software firewall and the Kerberos authentication server.

Part VI: The Part of Tens

You may already know that every For Dummies book has one of these parts. In it, you can find security tips, Internet traffic factoids, advice about places to go and things to do (even if you never leave your computer), and more security pointers. And all this happens in, roughly, sets of ten.

Icons Used in This Book

Signals nerdy technofacts that you can easily skip without hurting your TCP/IP education. But if you’re even a part-time techie, you probably love this stuff.

Indicates nifty shortcuts that make your life easier.

Lets you know that a loaded gun is pointed directly at your foot. Watch out!

Marks information that’s important to commit to memory. To siphon off the most important information in each chapter, just skim through these icons.

Marks important TCP/IP security issues. Lots of security icons are in this book.

Where to Go from Here

Check out the table of contents or the index and decide where you want to start. If you’re an information technology manager, you’re probably interested in buzzwords and you know why everyone is on the TCP/IP bandwagon. If you’re a system or network administrator, start with Chapter 2 or 4, where we describe the major protocols and what they do. Chapters 12, 14, 20, and 21 talk about Internet security — a topic that’s for everyone concerned that their personal data is at risk.

Or, you can just turn the pages one by one. We don’t mind. Really.

Part I

TCP/IP from Names to Addresses

In this part . . .

You can’t play the game if you don’t know the rules. And TCP/IP is the set of rules, or protocols, for networks. TCP/IP is the software underpinning of the Internet and its World Wide Web. TCP/IP also includes services and applications that work with the protocols. Before we get into the hairy details of the protocols themselves, we give you some background on the people and committees who decide the direction of TCP/IP’s growth. Did you know that you can be part of these groups? We tell you how. You also become familiar with TCP/IP and Internet buzzwords.

Part I then delves into the ingredients of the TCP/IP suite: the protocols and services themselves and IP addressing. You see how the protocols fit into the layers of the TCP/IP network model, and you take a look at the most important ones. TCP/IP is a suite because it consists of more protocols than the two it’s named for, plus a set of services and applications. The TCP/IP protocols, services, and applications in the suite work together just like the rooms in a hotel suite or the pieces in a furniture suite work together. The set of protocols is also referred to as a stack.

From there, we go into Internet addressing.

People love names. Computers love numbers. You’ll hear this in each part of this book.

If your computer is named Woodstock, for example, the Internet may think of it as 198.162.1.4. You get to see how to build and understand these numeric addresses. Also, if you’re worried because you think that the Internet is running low on addresses, Part I eases your worries by cluing you in to a couple of different ways to make IP addresses go further: subnetting and NAT (Network Address Translation).

Bear in mind that TCP/IP stays alive by morphing regularly — at times, daily. So, the list of protocols we describe here — the Internet’s rules — will be even longer by the time you read this book.

Chapter 1

Understanding TCP/IP Basics

In This Chapter

Protocols in this chapter: IP, TCP, IPSec, PPTP, L2TP

Introducing TCP/IP

Defining a protocol

Understanding RFCs — the protocol documentation

Differentiating between intranets, extranets, and Virtual Private Networks (VPNs)

Figuring out who’s in charge of TCP/IP and the Internet

Investigating different types of networks that rely on TCP/IP software

You bought or borrowed this book, or maybe you’re just flipping through it to pick up some information and tips about TCP/IP and its pieces and parts. Transmission Control Protocol/Internet Protocol, or TCP/IP, is the internationally accepted software for networking in general and, specifically, for making the Internet’s services possible.

As you read this book, you get a behind-the-scenes look at how TCP/IP makes the Internet work. You also see how to use TCP/IP to set up your own home, office, or even international network. This chapter gets started by defining a protocol in general and TCP/IP protocols specifically. Proposals known as Requests for Comment, or RFCs, document how TCP/IP should function. You may wonder who’s in charge of defining these protocols that rule the Internet. The answer is: lots of people who join international committees. This chapter describes the main Internet governing committees and what they do.

The Internet is one giant worldwide network that consists of tens of thousands of other networks. We give you an idea in this chapter of the different kinds of networks that connect via TCP/IP into the Internet.

The TCP/IP pronunciation guide

Pronouncing TCP/IP is easy — you just say the name of each letter and ignore the slash (/). Ready? It sounds like this:

“Tee cee pee eye pee”

Skip the silly jokes, please. We’ve made them all. By the way, some people find five letters too much to pronounce, so they just say “IP” to refer to the whole thing.

Following Rules for the Internet: TCP/IP Protocols

A protocol is a set of behavior-related rules that people follow. Some protocols are formally defined. For example, when people meet and greet each other, they might say, “Enchante de faire votre conaissance” or “How do you do”? We also hear our niece, Emily, and her friends saying “Hey, dude!” All these examples are widely accepted behaviors for people to start communicating — they are protocols. The more formal greetings are written down in etiquette books. “Hey, dude” has become accepted (at least by people much younger than we are) because of its wide use. Common ways of connecting aren’t enough, though. After you meet, you need a common language in order to communicate. Just as people connect and communicate in accepted ways, computers connect and communicate with each other and with you. In the world of computers and networks, TCP/IP is a common language used for both connection and communication.

Although TCP/IP sounds like it consists of just two protocols, it’s a whole set of protocols for connecting computers to the Internet. This set of protocols is the TCP/IP stack, or protocol suite. We describe in Chapter 2 the most well-known protocols in the TCP/IP stack. Before we get to the protocols themselves, the following sections look at who’s in charge of the Internet and who decides what gets to be a standard part of the TCP/IP protocol suite. You also get familiar with Requests for Comments (RFCs), the documents that describe TCP/IP standards.

Who’s in charge of the Internet and TCP/IP?

You’re in charge. Or, you might say that everyone is, and no one is, in charge of the Internet and TCP/IP. No one person, organization, corporation, or government owns or controls the TCP/IP protocols or the Internet. Moreover, no one person, organization, corporation, or government finances the TCP/IP protocols or the Internet. To say that no one controls TCP/IP and the Internet doesn’t mean, however, that protocols magically appear with no control or that the Internet just does whatever it wants.

This list describes some of the important organizations and committees that steer TCP/IP and Internet policies:

Internet Society (ISOC): The Internet Society (www.isoc.org) guides the future of the Internet by overseeing Internet standards, public policy, education, and training. ISOC members include corporations, international and governmental organizations, and individuals. The Internet Activities Board (refer to third bullet), the Internet Engineering Task Force (refer to fourth bullet), and the Internet Research Task Force are all part of the ISOC.

Internet Corporation for Assigned Names and Numbers (ICANN): The nonprofit corporation ICANN, at www.icann.org, is in charge of assigning Internet addresses. ICANN, pronounced “eye can,” is run by an international board of directors and funded by the Internet community.

Internet Activities Board (IAB): IAB, at www.iab.org, defines the architecture for the Internet. The IAB — just say its letters, “i-a-b” — also oversees the Internet’s protocols (TCP/IP). The IAB contains subcommittees of volunteers who set standards and work on new solutions to Internet growth problems.

Internet Engineering Task Force (IETF): IETF, at www.ietf.org, is a community of more than 70 informal committees responsible for keeping the Internet up and running every day. The IAB supervises the IETF, which is pronounced simply “i-e-t-f.” You can join the IETF working groups to help draft and develop standards for TCP/IP protocols.

Figure 1-1 shows how these Internet management groups are organized.

Figure 1-1: ISOC and ICANN are influential Internet steering groups.

Checking out RFCs: The written rules

TCP/IP protocols are written down in special Request for Comments (RFC) documents. An RFC (pronounced “r-f-c”) document is available for everyone to read and comment on — it’s part of the democracy of the Internet.

Toasting the RFC Editor

Surprise! The RFC Editor isn’t just one person. It consists of a small group of people who work for the Internet Society. The RFC Editor Web site, at www.rfc-editor.org, keeps the official index of all RFCs ever written. You can find any RFC there. We find this site to be one of the most useful when we want information about what’s going on with TCP/IP. You can search RFCs by number, author, title, or keyword. For example, click the link Search for an RFC and Its Meta-Data and then search for the keyword security. Notice how many pages it takes to display the results. And the list of results only grows — an RFC is never removed. It may be declared obsolete, but it stays available.

Knowing who writes RFCs

If you come up with an idea for a new or an improved capability for TCP/IP, you write your proposal as an RFC and submit it to an Internet committee for review. Working groups from various committees collaborate on most RFCs. You can join these working groups if you want to help but don’t want to write a whole RFC on your own. For example, to join an IETF working group, send an e-mail to [email protected].

Understanding RFC categories

Three categories of RFCs are on the standards track:

Standard (STD): An approved technical standard

Draft standard: On its way to being adopted as a standard

Proposed standard: On its way to being adopted as a draft standard

Here are some other RFC categories:

Best current practices (BCP): Guidelines and recommendations, such as RFC 4107, “Guidelines for Cryptographic Key Management”

Experimental (EXP): Part of a research or development project, such as RFC 5335, “Internationalized Email Headers”

Historic: Refers to the fact that most historic RFCs are former standards that are now obsolete and have been replaced by more current RFCs

Informational (FYI): Provides general information, such as RFC 4677, “The Tao of IETF — A Novice’s Guide to the Internet Engineering Task Force”

If you have time and a sense of humor, check out the RFCs written on April 1, but do not take them seriously!

Examining Other Standards Organizations That Add to the Rules

Although the Internet corporations, committees, and groups listed in the preceding section specify the rules for using TCP/IP, other groups set standards for related technologies, as described in this list:

Institute of Electrical and Electronics Engineers (IEEE): The IEEE (pronounce it “eye-triple-e”) sets hardware standards, such as the hardware that connects Local Area Networks (LANs) and Wireless Local Area Networks (WLANs).

WorldWide Web Consortium (W3C): Although the Web is part of the Internet and follows TCP/IP standards, the W3C (say the letters and number “w-c-3”) sets standards related to Web services.

International Organization for Standardization (ISO): ISO (“eye-so”) sets all kinds of standards, not just for networks. One of its standards indicates how the computers that run your car should interconnect.

Open Systems Interconnection (OSI): The OSI (“o-s-i”) sets networking protocol standards similar to TCP/IP, but different. At one time, OSI thought that its protocols would replace TCP/IP, but as hard as its members worked, it didn’t happen.

Free Software Foundation (FSF) General Public License (GPL): The FSF set up the GNU (pronounced “guh-new”) project to create and distribute free software. GNU software, licensed under the GPL, is the reason that the Linux operating system is available for free or for a very low cost. GNU also provides lots of network tools and utilities as well as complete TCP/IP stacks.

Distinguishing Between the Internet, an Internet, and an Intranet

Yes, we realize that you already know what the Internet is. But just so that we’re all using the same definition, the Internet is the worldwide collection of interconnected computer networks that use the TCP/IP protocol. These networks reach every continent — even Antarctica — and nearly every country.

The Internet also consists of much more than its network connections. It’s all the individual computers connected to those individual networks, plus all the users of those computers, all the information accessible to those users, and all the knowledge those people possess. The Internet is just as much about people and information as it is about computers and computer networks.

Although the Internet is public, many organizations (companies and universities, for example) have their own, private internets that may connect to it. An internet is built the same way as the Internet, except that an internet is private. You might even have an internet in your home.

Both the Internet and internets run on TCP/IP protocol software. In this book, we distinguish the Internet from an internet by capitalizing the Internet.

The difference between an internet and an intranet is just terminology. The term intranet is fairly recent. Old-timers (such as the authors of this book) grew up with “an internet” and now we use both terms. The important concept is that all kinds of “nets” run with TCP/IP.

Extending Intranets to Extranets

Intranets are the building blocks of extranets. If part of your intranet is available to people outside your organization, such as customers and suppliers, the part you share with the outside world is an extranet. An extranet has these characteristics:

It consists of multiple, interconnected intranets/internets.

An organization’s extended family of partners work together electronically.

It might not exist physically — it’s a virtual network.

Because an intranet is a private network within an organization or a department, you might find a few different intranets in a large institution. A university on the east coast, for example, might have one intranet for its medical school, another intranet for its college of liberal arts, and a third intranet for its business school. That university may also network those intranets into an even bigger intranet. Then, so that the university community can reach the rest of the world, the university intranet needs to be connected to the (capital I) Internet.

When that university needs to share data with a different university on the west coast, the two universities can link their respective intranets to create an extranet. Figure 1-2 shows how the east and west coast universities form an extranet.

Figure 1-2: Intranets link to form an extranet.

An extranet consists of as many intranets as you need in order to communicate with your partners.

Introducing Virtual Private Networks

A Virtual Private Network, or VPN (“v-p-n”), is a private network that runs over public facilities, such as the Internet. Although it may seem like a contradiction to run a private network over the (very) public Internet, it works. In the olden days of computers (which is often six months ago, but we’re talking as long as five years ago), if you wanted to work away from your office, you usually used a very slow modem to dial in across your phone line to the office computer. This method was slow and not secure because bad people could steal the data you were sending and receiving across the telephone lines.

Nowadays, most telecommuters connect to their offices through VPNs. They let you work as though you’re on-site when you’re not. You run VPN client software to establish a secure connection over the Internet to your organization’s network. It’s just like being in the office.

A VPN

Is safe and secure because it scrambles (encrypts) data before sending it over the public lines

Uses special tunneling and security protocols on the public network

See the section about the IPSec, PPTP, and L2TP protocols in Chapter 22 for more information.

Saves money for a large organization’s networks because sharing the public Internet is cheaper than leasing private telecommunication lines

Connects both intranets and extranets

The extranet shown earlier, in Figure 1-2, is also a VPN.

Exploring Geographically Based Networks

Whether you’re sending e-mail or browsing the Web, your data gets broken up into small pieces called packets. In other words, your data is “packetized” before it goes onto a network. Packets of data travel over many different kinds of geographical distances, ranging from local to global and beyond to space. TCP/IP doesn’t care about earthly distance — just that your data gets where it’s going. In this section, get ready for a lot of jargon-y terms that look a lot alike. If you aren’t interested in network architecture, feel free to skip this section and save your brain from getting muddled.

Networks connected by wires and cables

Networks come in different shapes and sizes. Two main architectures for networks — LANs (Local Area Networks) and WANs (Wide Area Networks) — are usually based on these factors:

The distance the network covers

Architecture and connection media

Speed

Purpose

(For example, does the network connect a city, a campus, or just a bunch of storage devices?)

Exploring LANs

Pronounce LAN as a word — “lan” (rhymes with “pan”). The computers and other devices in a LAN communicate over small geographical areas, such as these:

Your home office — or even the whole house

One wing of one floor in a building

Maybe the entire floor, if it’s a small building

Several buildings on a small campus

Incorporating WANs

Imagine a company that has several buildings in different towns and provinces, or even in different countries. Does that mean that all the people who work in the company can’t be on the same network because a LAN is limited by distance? Of course not. The Internet is worldwide and beyond, so you can even bounce data off satellites in outer space, to create a WAN.

A WAN (“wan”) spans geographical distances that are too large for LANs. Figure 1-3 shows two LANs connected to form a WAN.

Wireless networks

You don’t need cables and wires to connect the computers that comprise a network. You can go wireless, and cables can be expensive. (Air, a wireless connection media, is free — at least for now.) Just as cabled LANs and WANs exist, wireless LANs (WLANs) and wireless WANs (WWANS) also exist.

You pronounce WLAN as the letter w followed by the word LAN: “double-you-lan.” Pronounce WWAN as the letter w followed by the word WAN: (“double-you wan”).

Although the following network technologies differ, your packets of data can fly through the air faster than Superwoman:

WLAN: Uses radio waves to connect computers and networks. It shows up in homes, cafés, malls — even whole cities.

WWAN: WWANs are based on telecommunications (mobile cellular networks) and use Worldwide Interoperability for Microwave Access (WiMAX) technology. A WWAN lets anyone with a computer work anywhere within a mobile phone network.

The geography of TCP/IP

TCP/IP fits everywhere. Regardless of your geographical network technology, in the end it’s TCP/IP that carries your data, such as e-mail or Web pages, to you.

Figure 1-3: A special piece of hardware converts two LANs into a WAN.

Chapter 2

Layering TCP/IP Protocols

In This Chapter

Taking a quick look at some network hardware

Examining the TCP/IP layered approach

Watching packets munch through the TCP/IP layers

Discovering that TCP/IP consists of much more than just two protocols

Investigating the major protocols and services that make up TCP/IP

If you already read Chapter 1, you know that a protocol is the set of agreed-on practices, policies, and procedures used for communication. In this book, we look at TCP/IP as the protocol set for communication between two or more computers. Remember that TCP/IP is a large suite of components that work together. In this chapter, we first describe the layered TCP/IP organization and then the protocols themselves.

TCP/IP technology is designed to allow all parts of your network to work together, regardless of which suppliers you bought them from. To make your network parts cooperate, TCP/IP divides network functions (for example, sending data or connecting different computer hardware) into layers and defines how those layers should interact.

Taking a Timeout for Hardware

There’s no point in having software if you have no hardware on which to run it. Although TCP/IP protocols are software, we need to discuss network connection media and Ethernet — the most widely used local-area network (LAN) technology on the Internet. Talking about software without occasionally mentioning hardware is almost impossible, so we mention Ethernet in the following sections of this chapter and in other chapters in this book.

Starting with network connection media

Suppose that you want to connect all your networked devices — computers, printers, mobile phone, television, and game system — on your home network. Connection media and devices include much more than cables and wires. You can connect devices by using wireless access points, fiber optics, microwaves, infrared signals, and signals beamed to and from satellites.

The most important connection device is the network interface card (or NIC, also known as a network adapter or a network card). This computer circuit board (or card, for short) lets your computer be connected to a network by cables or air. The NIC converts data into electrical signals. Most computers come with a NIC, either wireless or wired or both, already installed inside the case. The NIC’s manufacturer hardcodes on every NIC a unique hardware address known as the Media Access Control (MAC). Some protocols access this address. Figure 2-1 shows an example of a NIC with its MAC highlighted. Your card may look a little different, but all NICs function exactly the same.

Figure 2-1: Every NIC has a unique MAC address.

Colliding with Ethernet

Ethernet is by far the most widely used LAN technology. (See the nearby sidebar, “How fast can Ethernet go?”) Ethernet hardware ranges from fat, orange cables to plain old air. Ethernet allows any device on a network, from a giant corporate database server to the cash register in the local delicatessen, to send and receive packetized data.

How fast can Ethernet go?

The IEEE defines different kinds of Ethernet, depending on the connection media and the speed at which Ethernet moves the network data. In an Ethernet LAN, devices connect to the bus, not to each other. When the first edition of this book was written, Ethernet transmitted 1 gigabit (1 billion bits) of data across the network per second. That’s equal to 125 megabytes. Fast, huh? Ethernet can now move data at 10 gigabits per second. If you do the math, you see lots of zeros. Wait — there’s more! An IEEE group working on faster Ethernet is developing standards for 40 gigabits per second and 100 gigabits per second.

Ethernet uses the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) technique. This very long name has a simple meaning: When a network device realizes that a packet collision has occurred, it knows when to wait and retry. With Ethernet, the data from the small deli’s cash register is just as important as anything that the headquarters’ big server has to send. All devices on the network are equal. You see in Figure 2-2 a basic LAN connected by Ethernet. Each device on the network, including the printer, has a NIC and TCP/IP software running.

Figure 2-2: Ethernet watches for collisions in a very small LAN.

Stacking the TCP/IP Layers

TCP/IP software organizes the protocols in layers so that five layers are stacked up in the TCP/IP model. We love desserts and snacks, so we like to describe TCP/IP as a five-layer cake. Figure 2-3 gives you an idea of how the layers are structured.

Figure 2-3: Check out these “yummy” layers.

Technically, the five layers in the “cake” comprise a stack, and the protocols that sit in these layers comprise a protocol stack.

Each layer of the stack depends on the layers below it; that is, each layer services the layer above or below it. When two computers communicate, each computer has its own set of layers. When you send a message to another computer on the network, your information starts at the top layer of your computer, travels down all the layers to the bottom of the stack, and then jumps to the other computer. When your information arrives on the other computer, it starts at the bottom layer and moves up the stack to the application in the top layer.

Each layer has a special function: The lower layers are hardware oriented, and the highest layer provides user services, such as e-mail, file transfers, and general network monitoring. Look at Figure 2-4 to see how data moves through these layers.

In the following sections, we examine each layer, starting with Layer 1, at the bottom of the cake.

How many TCP/IP stacks exist?

The answer is “only one, yet many.” Or, “It depends.” Only one set of standards exists for a TCP/IP stack. Those standards come from RFCs, described in Chapter 1. On the other hand, the protocols, services, and applications are software programs. Somebody has to write the programs to implement TCP/IP software. And — oh, boy! — are there ever a lot of somebodies. A TCP/IP stack usually is supplied with your computer. If you buy a computer that runs a version of Microsoft Windows, a team of Microsoft programmers most likely wrote the programs that make your computer’s stack run. If your computer is a Mac, Apple Computer programmers wrote the stack. It doesn’t matter who wrote the TCP/IP stack. What’s important is that the programs work the way they’re supposed to, according to the RFCs.

Most Linux and Unix operating systems (and there are so many) have built-in TCP/IP protocol stacks.

If you don’t like the way your stack is programmed, you can swap in another stack. Even better, you can download and swap in a free stack, or just part of a stack, from the Internet. If you search for the phrase free software TCP/IP at www.google.com, you see a long list of TCP/IP programs.

Figure 2-4: Data travels up and down through each layer.

Layer 1: The physical layer

The physical layer at the bottom of the stack is pure hardware, including the cable or satellite (or other) connection medium and the network interface card. This layer is where electrical signals move around (and we try not to think too hard about how it works). Protocols in the two bottom hardware layers aren’t part of the TCP/IP stack. The physical layer transforms data into bits that move across the network media. The protocols in the physical layer include protocols related to cables, or to air, in the case of wireless. The physical layer also has protocols for connection methods.

Layer 2: The data link layer

This layer is another one that we don’t want to strain our brains trying to figure out — again, hardware is involved. This layer splits data into packets to be sent across the connection medium, and then wiring, such as Ethernet or token ring, gets involved. The data link layer moves data up through the higher layers for transportation across networks and through tunnels to Virtual Private Networks (VPNs).

The data link layer also includes protocols that work with your Media Access Control (MAC) address and your network interface card (NIC).

A MAC address is a hardwired special address on your NIC. Every NIC has a unique MAC address.