Charles M. Kozierok The TCP-IP Guide

Подождите немного. Документ загружается.

List of Tables

Table 1: Version History.................................................................................................55

Table 2: Binary Information Group Representations and Terms .............................121

Table 3: Binary and Decimal Number Equivalents ....................................................124

Table 4: Binary, Octal and Hexadecimal Digit Conversion .......................................127

Table 5: Hexadecimal to Decimal Number Conversion.............................................128

Table 7: Decimal to Hexadecimal Number Conversion.............................................130

Table 6: Decimal to Binary Number Conversion........................................................130

Table 8: Binary Addition...............................................................................................131

Table 9: Hexadecimal Addition....................................................................................132

Table 10: NOT Operator Truth Table...........................................................................133

Table 11: NOT Operator Truth Table (Using Bit Values) ...........................................134

Table 12: AND Operator Truth Table...........................................................................134

Table 13: OR Operator Truth Table .............................................................................134

Table 14: Exclusive OR (XOR) Operator Truth Table ................................................135

Table 15: Setting Bits Using an OR Bit Mask .............................................................137

Table 17: Inverting Bits Using an XOR Bit Mask........................................................138

Table 16: Clearing Bits Using an AND Bit Mask ........................................................138

Table 18: OSI Reference Model Real-World Analogy ................................................165

Table 19: OSI Reference Model Layer Summary .......................................................184

Table 20: TCP/IP Protocols: Network Interface Layer (OSI Layer 2) ........................199

Table 21: TCP/IP Protocols: Network Interface / Network Layer

(“OSI Layer 2/3”).................................................................................................199

Table 22: TCP/IP Protocols: Network Layer (OSI Layer 3) ........................................200

Table 23: TCP/IP Protocols: Host-to-Host Transport Layer (OSI Layer 4)...............201

Table 24: TCP/IP Protocols: Application Layer (OSI Layer 5/6/7).............................201

Table 25: PPP Phases...................................................................................................223

Table 26: PPP Base Standards....................................................................................224

Table 27: PPP LCP Support Protocol Standards .......................................................225

Table 28: PPP Network Control Protocol Standards .................................................225

Table 29: PPP Feature Protocol Standards................................................................226

Table 30: PPP Application and Miscellaneous Standards ........................................226

Table 31: PPP Compression Control Protocol (CCP) Compression

Algorithms...........................................................................................................244

Table 32: PPP Encryption Control Protocol (ECP) Encryption Algorithms ............247

Table 33: PPP General Frame Format.........................................................................255

Table 34: PPP Protocol Field Ranges .........................................................................257

Table 35: Common Protocols Carried In PPP Frames and Protocol Field

Values ..................................................................................................................258

Table 36: PPP Control Message Format.....................................................................260

Table 37: PPP Control Messages, Code Values and PPP Protocol Usage..............262

Table 38: PPP Control Message Option Format ........................................................263

Table 39: PPP Link Control Protocol (LCP) Frame Types and Fields......................265

Table 40: PPP Password Authentication Protocol (PAP) Frame Formats...............268

Table 41: PPP Challenge Handshake Authentication Protocol (CHAP)

Formats ...............................................................................................................270

Table 42: PPP Multilink Protocol Fragment Frame Format.......................................272

Table 43: Address Resolution Protocol (ARP) Message Format .............................294

Table 44: IP Address Classes and Class Characteristics and Uses ........................335

Table 45: IP Address Class Bit Patterns, First-Octet Ranges and Address

Ranges.................................................................................................................339

Table 46: IP Address Class Network and Host Capacities .......................................342

Table 47: IP Address Patterns With Special Meanings .............................................344

Table 48: Reserved, Loopback and Private IP Addresses ........................................347

Table 49: IP Multicast Address Ranges and Uses .....................................................349

Table 50: Well-Known IP Multicast Addresses ..........................................................350

Table 51: Determining the Subnet ID of an IP Address Through Subnet

Masking ...............................................................................................................361

Table 52: Default Subnet Masks for Class A, Class B and Class C Networks ........365

Table 53: Subnetting Summary Table For Class A Networks...................................374

Table 54: Subnetting Summary Table For Class B Networks...................................376

Table 55: Subnetting Summary Table For Class C Networks...................................377

Table 56: CIDR Address Blocks and “Classful” Address Equivalents....................410

Table 57: Internet Protocol Version 4 (IPv4) Datagram Format................................420

Table 58: Original Definition Of IPv4 Type Of Service (TOS) Field ..........................424

Table 59: Internet Protocol Version 4 (IPv4) Option Format.....................................426

Table 60: Internet Protocol Version 4 (IPv4) Options................................................427

Table 61: IPv6 Address Space Allocations.................................................................471

Table 62: Generic IPv6 Global Unicast Address Format...........................................474

Table 63: IPv6 Global Unicast Address Format .........................................................474

Table 64: Historical IPv6 Unicast Routing Prefix Structure ......................................476

Table 65: Example IPv6 Unicast Routing Prefix Structure........................................477

Table 66: IPv6 Multicast Address Format...................................................................487

Table 67: Important IPv6 “Well-Known” Multicast Addresses .................................489

Table 68: IPv6 General Datagram Structure...............................................................496

Table 69: IPv6 Main Header Format ............................................................................497

Table 70: Common IPv6 Next Header Values.............................................................499

Table 71: IPv6 Extension Headers...............................................................................503

Table 72: IPv6 Routing Extension Header Format.....................................................504

Table 73: IPv6 Fragment Extension Header Format..................................................505

Table 74: IPv6 Option Format ......................................................................................508

Table 75: Operation Of Unidirectional (Traditional/Outbound) NAT ........................529

Table 76: Operation Of Bidirectional (Two-Way/Inbound) NAT................................533

Table 77: Operation Of Port-Based (“Overloaded”) NAT ..........................................537

Table 78: Operation Of “Overlapping” NAT / “Twice NAT” ......................................541

Table 79: Important IP Security (IPSec) Standards ...................................................547

Table 80: IPSec Authentication Header (AH) Format ................................................563

Table 81: IPSec Encapsulating Security Payload (ESP) Format ..............................568

Table 82: Mobile IP Mobility Agent Advertisement Extension Format ....................586

Table 83: Mobile IP Prefix-Lengths Extension Format ..............................................588

Table 84: Mobile IP Registration Request Message Format.....................................592

Table 85: Mobile IP Registration Reply Message Format .........................................593

Table 86: Non-ICMP Internet Standards That Define ICMP Messages.....................607

Table 87: ICMP Message Classes, Types and Codes................................................612

Table 88: ICMP Common Message Format ................................................................617

Table 89: ICMPv4 Destination Unreachable Message Format..................................621

Table 90: ICMPv4 Destination Unreachable Message Subtypes..............................622

Table 91: ICMPv4 Source Quench Message Format .................................................625

Table 92: ICMPv4 Time Exceeded Message Format..................................................628

Table 93: ICMPv4 Redirect Message Format..............................................................631

Table 94: ICMP Redirect Message Interpretation Codes...........................................632

Table 95: ICMPv4 Parameter Problem Message Format ...........................................633

Table 96: ICMPv4 Parameter Problem Message Interpretation Codes ....................634

Table 97: ICMPv4 Echo and Echo Reply Message Format .......................................637

Table 98: ICMPv4 Timestamp and Timestamp Reply Message Format...................639

Table 99: ICMPv4 Router Advertisement Message Format ......................................641

Table 100: ICMPv4 Router Solicitation Message Format ..........................................643

Table 101: ICMPv4 Address Mask Request and Address Mask Reply

Message Format .................................................................................................645

Table 102: ICMPv4 Traceroute Message Format .......................................................647

Table 103: ICMPv6 Destination Unreachable Message Format................................650

Table 104: ICMPv6 Destination Unreachable Message Subtypes............................651

Table 105: ICMPv6 Packet Too Big Message Format ................................................652

Table 106: ICMPv6 Time Exceeded Message Format................................................656

Table 107: ICMPv6 Parameter Problem Message Format .........................................658

Table 108: ICMPv6 Parameter Problem Message Interpretation Codes ..................659

Table 109: ICMPv6 Echo Request and Echo Reply Message Format ......................661

Table 110: ICMPv6 Router Advertisement Message Format ....................................663

Table 111: ICMPv6 Router Solicitation Message Format ..........................................665

Table 112: ICMPv6 Neighbor Advertisement Message Format ................................667

Table 113: ICMPv6 Neighbor Solicitation Message Format......................................669

Table 114: ICMPv6 Redirect Message Format............................................................671

Table 115: ICMPv6 Router Renumbering Message Format ......................................674

Table 116: ICMPv6 Source Link-Layer Address Option Format...............................677

Table 117: ICMPv6 Target Link-Layer Address Option Format ................................678

Table 118: ICMPv6 Prefix Information Option Format...............................................679

Table 119: ICMPv6 Redirected Header Option Format..............................................681

Table 120: ICMPv6 MTU Option Format......................................................................681

Table 121: RIP Version 1 (RIP-1) Message Format ....................................................724

Table 122: RIP Version 2 (RIP-2) Message Format ....................................................728

Table 123: RIPng Message Format..............................................................................731

Table 124: Example OSPF Link State Database (LSDB) ...........................................737

Table 125: Example OSPF Link State Database (LSDB) With Costs........................742

Table 126: Example Calculated OSPF Routes ...........................................................745

Table 127: OSPF Common Header Format.................................................................748

Table 128: OSPF Hello Message Format ....................................................................749

Table 129: OSPF Database Description Message Format ........................................750

Table 130: OSPF Link State Request Message Format.............................................752

Table 131: OSPF Link State Update Message Format...............................................753

Table 132: OSPF Link State Acknowledgment Message Format .............................754

Table 133: OSPF Link State Advertisement Header Format .....................................755

Table 134: Border Gateway Protocol (BGP) Versions and Defining

Standards ............................................................................................................768

Table 135: Additional Defining Standards For BGP-4 ...............................................769

Table 136: Summary of BGP Path Attributes .............................................................779

Table 137: BGP General Message Format..................................................................786

Table 138: BGP Open Message Format......................................................................788

Table 139: BGP Update Message Format ...................................................................791

Table 140: Details of BGP Update Message Attribute Type Subfield ......................794

Table 141: BGP Keepalive Message Format ..............................................................797

Table 142: BGP Notification Message Format ...........................................................798

Table 143: BGP Notification Message Error Codes...................................................799

Table 144: BGP Notification Message Error Subcodes.............................................800

Table 145: TCP and UDP Port Number Ranges .........................................................818

Table 146: Common TCP/IP Well-Known Port Numbers and Applications.............824

Table 147: Common TCP/IP Registered Port Numbers and Applications...............825

Table 148: UDP Message Format ................................................................................830

Table 149: Common UDP Applications and Server Port Assignments ...................834

Table 150: Supplementary TCP Standards.................................................................839

Table 151: Common TCP Applications and Server Port Assignments....................862

Table 152: TCP Finite State Machine (FSM) States, Events and Transitions ..........866

Table 153: TCP “Three-Way Handshake” Connection Establishment

Procedure............................................................................................................873

Table 154: TCP Simultaneous Open Connection Establishment Procedure ..........875

Table 155: TCP Connection Termination Procedure .................................................884

Table 156: TCP Simultaneous Connection Termination Procedure ........................887

Table 157: TCP Segment Format.................................................................................890

Table 158: TCP Options................................................................................................894

Table 159: TCP “Pseudo Header” For Checksum Calculation .................................896

Table 160: TCP Transaction Example With Send and Receive Pointers .................907

Table 161: Summary Comparison of UDP and TCP ..................................................945

Table 162: Example TCP/IP Host Table.......................................................................967

Table 163: Documents Discussing TCP/IP Domain Name System (DNS)

Concepts .............................................................................................................973

Table 164: Initial Standards Defining The TCP/IP Domain Name System

(DNS)....................................................................................................................973

Table 165: Additional DNS Standards.........................................................................974

Table 166: Internet DNS Organizational (Generic) Top-Level Domains...................997

Table 167: Summary Of Common DNS Resource Records ....................................1019

Table 168: Internet DNS Root Name Servers ...........................................................1028

Table 169: DNS General Message Format ................................................................1058

Table 170: DNS Message Header Format .................................................................1061

Table 171: DNS Message Question Section Format................................................1065

Table 172: DNS Common Resource Record Format ...............................................1067

Table 173: DNS Address Resource Record Data Format........................................1068

Table 174: DNS Name Server Resource Record Data Format ................................1068

Table 175: DNS Canonical Name Resource Record Data Format ..........................1068

Table 176: DNS Start Of Authority Resource Record Data Format........................1069

Table 177: DNS Pointer Resource Record Data Format..........................................1070

Table 178: DNS Mail Exchange Resource Record Data Format .............................1071

Table 179: DNS Text Resource Record Data Format...............................................1071

Table 180: DNS Master File Format Syntax and Examples.....................................1077

Table 181: Sample DNS Master File ..........................................................................1078

Table 182: NFS External Data Representation (XDR) Data Types..........................1090

Table 183: NFS Version 2 and Version 3Server Procedures ..................................1094

Table 184: NFS Version 4 Server Procedures ..........................................................1096

Table 185: NFS Version 4 Server Operations...........................................................1097

Table 186: NFS Mount Protocol Server Procedures................................................1100

Table 187: BOOTP Message Format .........................................................................1115

Table 188: BOOTP Vendor Information Field Format..............................................1121

Table 189: DHCP Client Finite State Machine ..........................................................1149

Table 190: DHCP Message Format............................................................................1173

Table 191: DHCP Option Format ...............................................................................1177

Table 192: DHCP Option Categories.........................................................................1179

Table 193: DHCP/BOOTP Options: RFC 1497 Vendor Extensions.........................1181

Table 194: DHCP/BOOTP Options: IP Layer Parameters Per Host ........................1183

Table 195: DHCP/BOOTP Options: IP Layer Parameters Per Interface .................1184

Table 196: DHCP/BOOTP Options: Link Layer Parameters Per Interface .............1184

Table 197: DHCP/BOOTP Options: TCP Parameters...............................................1185

Table 198: DHCP/BOOTP Options: Application and Service Parameters .............1185

Table 199: DHCP Options: DHCP Extensions ..........................................................1188

Table 200: SNMP Version 1 (SNMPv1) Standards ...................................................1218

Table 201: SNMP Security (SNMPSec) Standards ...................................................1218

Table 202: Party-Based SNMP Version 2 (SNMPv2p) Standards ...........................1218

Table 203: Community-Based SNMP Version 2 (SNMPv2c) Standards.................1219

Table 204: User-Based SNMP Version 2 (SNMPv2u) Standards ............................1220

Table 205: SNMP Version 3 (SNMPv3) Standards ...................................................1220

Table 206: SNMP SMI Version 2 Max-Access Values ..............................................1228

Table 207: SNMP SMI Regular Data Types ...............................................................1229

Table 208: Example SNMP SMIv2 Object Definition ................................................1230

Table 209: SNMP Generic MIB Object Groups .........................................................1235

Table 210: Some Common SNMP MIB Modules ......................................................1237

Table 211: SNMP PDU (Message) Classes ...............................................................1244

Table 212: SNMP Variable Binding Format ..............................................................1260

Table 213: SNMP Version 1 (SNMPv1) General Message Format ..........................1261

Table 214: SNMP Version 1 (SNMPv1) Common PDU Format................................1262

Table 215: SNMP Version 1 (SNMPv1) Trap-PDU

Format .......................................1264

Table 216: SNMP Version 2 (SNMPv2p) General Message Format ........................1266

Table 217: Community-Based SNMP Version 2 (SNMPv2c) General

Message Format ...............................................................................................1268

Table 218: User-Based SNMP Version 2 (SNMPv2u) General Message

Format ...............................................................................................................1269

Table 219: SNMP Version 2 (SNMPv2) Common PDU Format................................1271

Table 220: SNMP Version 2 (SNMPv2) PDU Error Status Field Values..................1272

Table 221: SNMP Version 2 (SNMPv2) GetBulkRequest-PDU Format ...................1273

Table 222: SNMP Version 3 (SNMPv3) General Message Format ..........................1277

Table 223: SNMP RMON MIB Object Groups ...........................................................1281

Table 224: URL Special Character Encodings .........................................................1291

Table 225: Relative URL Specifications and Absolute Equivalents.......................1299

Table 226: FTP Access Control Commands.............................................................1336

Table 227: FTP Transfer Parameter Commands ......................................................1337

Table 228: FTP Service Commands ..........................................................................1337

Table 229: FTP Reply Code Format: First Digit Interpretation ...............................1340

Table 230: FTP Reply Code Format: Second Digit Interpretation ..........................1340

Table 231: FTP Reply Codes......................................................................................1342

Table 232: FTP Multiple-Line Text Reply Example ..................................................1344

Table 233: FTP User Commands ...............................................................................1346

Table 234: Sample FTP Session................................................................................1348

Table 235: TFTP Options............................................................................................1363

Table 236: TFTP Read Request / Write Request Message Format.........................1364

Table 237: TFTP Data Message Format ....................................................................1365

Table 238: TFTP Acknowledgment Message Format ..............................................1366

Table 239: TFTP Error Message Format ...................................................................1367

Table 240: TFTP Option Acknowledgment Message Format..................................1368

Table 241: RFC 822 Electronic Mail Header Field Groups and Fields ...................1393

Table 242: Multipurpose Internet Mail Extensions (MIME) Standards ...................1401

Table 243: MIME text Media Type Subtypes.............................................................1407

Table 244: MIME image Media Type Subtypes.........................................................1408

Table 245: MIME audio Media Type Subtypes..........................................................1408

Table 246: MIME video Media Type Subtypes..........................................................1408

Table 247: MIME model Media Type Subtypes.........................................................1409

Table 248: MIME application Media Type Subtypes ................................................1410

Table 249: Example MIME Multipart Message..........................................................1415

Table 250: MIME Base64 Encoding Groups .............................................................1418

Table 251: Example SMTP Mail Transaction ............................................................1433

Table 252: SMTP Extensions .....................................................................................1435

Table 253: SMTP Commands.....................................................................................1439

Table 254: SMTP Reply Code Format: First Digit Interpretation ............................1442

Table 255: SMTP Reply Code Format: Second Digit Interpretation .......................1443

Table 256: SMTP Reply Codes...................................................................................1443

Table 257: Example POP3 Authorization..................................................................1455

Table 258: POP3 Transaction Commands................................................................1457

Table 259: Example POP3 Mail Exchange Process .................................................1460

Table 260: IMAP “Any State” Commands.................................................................1470

Table 261: IMAP Not Authenticated State Commands ............................................1473

Table 262: IMAP Authenticated State Commands ...................................................1474

Table 263: IMAP Selected State Commands ............................................................1477

Table 264: Usenet “Big Eight” Newsgroup Hierarchies..........................................1491

Table 265: Usenet Header Categories and Headers ................................................1496

Table 266: Common Additional Usenet Headers .....................................................1498

Table 267: NNTP Base Commands ...........................................................................1510

Table 268: NNTP Transport Extensions....................................................................1512

Table 269: NNTP LIST Command Extensions ..........................................................1513

Table 270: NNTP Newsreader Extensions................................................................1514

Table 271: NNTP Reply Code Format: First Digit Interpretation ............................1517

Table 272: NNTP Reply Code Format: Second Digit Interpretation .......................1518

Table 273: NNTP Reply Codes...................................................................................1519

Table 274: Common Hypertext Markup Language (HTML) Elements ....................1530

Table 275: HTTP Status Code Format: First Digit Interpretation............................1560

Table 276: HTTP Status Codes ..................................................................................1561

Table 277: HTTP Cache-Control Directives ..............................................................1566

Table 278: HTTP Warning Header Codes .................................................................1569

Table 279: Example HTTP Response Using Content-Length Header ....................1586

Table 280: Example HTTP Response Using Chunked Transfer Encoding............1586

Table 281: Interpretation of Standard Telnet NVT ASCII Control Codes ...............1616

Table 282: Telnet Protocol Commands.....................................................................1619

Table 283: Common Telnet Options..........................................................................1623

Table 284: Using the hostname Utility To Check A Host Name .............................1637

Table 285: Verifying Communication Using the ping Utility...................................1640

Table 286: Common UNIX ping Utility Options and Parameters ............................1641

Table 287: Common Windows ping Utility Options and Parameters.....................1642

Table 288: Route Tracing Using the traceroute Utility ............................................1646

Table 289: Common UNIX traceroute Utility Options and Parameters ..................1647

Table 290: Common Windows tracert Utility Options and Parameters .................1647

Table 291: DNS Name Resolution Using the nslookup Utility ................................1650

Table 292: Typical nslookup Utility Commands ......................................................1651

Table 293: DNS Name Resolution Using the host Utility ........................................1652

Table 294: Typical host Utility Options and Parameters.........................................1653

Table 295: DNS Name Resolution Using the dig Utility...........................................1654

Table 296: DNS Domain Registry Lookup Using the whois Program....................1656

Table 297: Typical UNIX netstat Option Groups, Options and Parameters...........1658

Table 298: Typical UNIX netstat Universal Options and Parameters.....................1659

Table 299: Sample Connections List From UNIX netstat Utility .............................1660

Table 300: Sample IP Statistics From UNIX netstat Utility......................................1661

Table 301: Typical Windows netstat Option Groups, Options and

Parameters ........................................................................................................1662

Table 302: Typical Windows netstat Universal Options and Parameters..............1662

Table 303: Sample ICMP Statistics From Windows netstat Utility .........................1663

Table 304: Sample Routing Table Display From Windows netstat Utility .............1663

Table 305: Typical UNIX ifconfig Syntaxes, Options and Parameters ...................1665

Table 306: Typical UNIX

ifconfig Universal Options and Parameters....................1665

Table 308: Sample Routing Table Display From Windows netstat Utility .............1666

Table 307: Typical UNIX ifconfig Interface Configuration Parameters ..................1666

Table 309: Typical Windows ipconfig Options and Parameters.............................1667

Table 310: Simplified Configuration Information From Windows ipconfig

Utility..................................................................................................................1668

Table 311: Detailed Configuration Information From Windows ipconfig

Utility..................................................................................................................1668

Table 312: Miscellaneous TCP/IP Troubleshooting Protocols ...............................1670

The TCP/IP Guide: Introduction and "Guide To The

Guide"

Chances are pretty good that even before you started reading this Guide, you had heard of

“TCP/IP”—even if you didn't know exactly what it was or even what all those letters stood

for. The reason for this is simple: TCP/IP is everywhere! It is today by far the most

commonly-used internetworking protocol suite. It has gained prominence in large part due

to its role in operating the global Internet, which has in a few short years transformed our

society in so many ways. Millions of people use TCP/IP and the Internet without really

knowing how they work. For those in the technology field, however, understanding TCP/IP

is becoming more important with each passing year.

As we journey together through this TCP/IP Guide, we will explore many hundreds of pages

of material that will explain both the generalities and specifics of TCP/IP in a way that I hope

you will find educational and interesting. Before diving into the actual technology, however, I

felt that I should provide you with some introductory material to help frame the discussions

that follow. Thus, I have included this section, to serve as an introduction to this Guide and

to provide some information that will help you use it to its full potential.

I begin with some material that will be of interest to those who want to know the background

of The TCP/IP Guide. I provide a general introduction to the Guide, describing its history,

and how it came about. I then describe the goals of this Guide and what I was trying to

accomplish in writing it. I also discuss the scope of the Guide, so you know what it covers

and what it does not.

The rest of the section contains more practical information to help you best utilize this rather

large document. I explain how the Guide is structured and organized, and discuss its

special features. I then provide some specific tips to help you navigate the Guide using the

Adobe Acrobat Reader software you are likely using at this moment. ☺ I also explain how

you can provide feedback on the Guide and suggestions for improving it, and I conclude

with a summary of the Guide’s version history.

Note: There is no actual technical content in this section. If you are the type who

buys something and starts using it right away without cracking open the manual,

you may want to skip this section. If so, you should start by looking at the high-

level discussion of the TCP/IP protocol suite; alternately, you may wish to begin at the

Networking Fundamentals section or with a look at the OSI Reference Model. However, I do

recommend at least skimming the topics in this section before you move on, especially the

topics discussing the structure and organization of the Guide and its features. This will

make the rest of the Guide easier to understand and probably save you time in the long run.

Introduction To The TCP/IP Guide

As I sit here writing this introductory material a few weeks before finishing off a multi-year

project culminating in this TCP/IP Guide, I reflect on how funny life can be. Prior to a few

years ago, I never really thought of myself as a writer. I have no training as an author, and

my interests have always been in computers. I always assumed that I would end up in a

technical job, such as computer programming or hardware design.

Perhaps ironically, then, it was my interest in personal computers that led to my writing The

PC Guide in 1997. After I put the first version of that site online, I received many compli-

ments on its usefulness. This didn’t surprise me, since the material was of course designed

to be useful. ☺ What shocked me were all the comments I received about how people

appreciated my writing. They said they found my material easy to understand, and some

said they had even read through textbooks but never understood the concepts they

explained until they encountered my site. I discovered that I perhaps I had a talent I had

never before considered; more, I realized that it felt good to dissect a difficult technical

subject and help people understand it.

In early 2001 I decided that I wanted to embark on a new writing project to go along with the

PC materials I had written in The PC Guide. I felt then, as I do now, that the future of infor-

mation technology lies not so much in bigger and faster computers, but in better ways of

exchanging information between them. I wanted to know more about networking and inter-

networking. So, I decided to create a Networking Guide to complement my PC Guide. I

thought that this would take about six months.

Remember what I said above about life being funny? ☺ Well, as soon as I embarked on my

project to create a Networking Guide, I realized that I had opened a virtual Pandora’s Box. I

had never realized just how large a topic networking was; there were literally hundreds of

different protocols, technologies, algorithms, concepts and devices to learn about. These

were all interconnected in a myriad of ways, and it was hard to explain how one protocol or

technology worked without first explaining another one. The amount of complexity was

amazing.

To make matters worse, I found that it was very hard to find information about networks that

really explained how everything worked. This seemed like an opportunity to me—I decided

that since so many people felt I did a good job explaining PC technology, that I should take

a crack at networking. Once I accepted that it would take more than six months, I figured I

should plan on up to two years to get this writing project completed. Well... life is even

funnier than I imagined. ☺ Fast forward from early 2001 to August 2003, and I find myself at

my desk, looking over my writing project. I realize that I have been at this now for two-and-

a-half years, yet due to my desire to cover as much as possible, I have at least a year’s

more work to go.

I began to feel burnt out from working on this new Networking Guide for such a long time,

during which it has existed only in my mind and on my PC’s hard disk drive. Even though

part of me wanted to wait to finish the entire Networking Guide and publish it all at once, a

larger part of me felt the need to publish at least some of what I had already written. I looked