Charles M. Kozierok The TCP-IP Guide

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Enabling Bookmarks

When you open The TCP/IP Guide, a pane should automatically appear on the left side that

shows the contents of the document in a hierarchical structure identical to the structure of

the Guide itself. Use these bookmarks to navigate the Guide and jump to topics of interest.

If for whatever reason the bookmarks are not displayed, click the vertical “Bookmarks” tab

on the upper left of the document area to show them, or select the “View” menu, then

“Navigation Tabs”, then “Bookmarks”.

Wrapping Long Bookmarks

Some of the section and topic titles in The TCP/IP Guide are quite long, and by default, you

may only be able to see the first few words of each in the bookmarks area. To see the full

title, click on the “Options” drop-down box in the bookmarks window, then select “Wrap

Long Bookmarks”.

Jumping To A Particular Page

Most often, you will find that it is easiest to jump to a particular section or topic using the

bookmarks, the Table of Contents or text hyperlinks. However, you can also go to a specific

page number manually. Either click on the current page number near the bottom of the page

and enter the number of the page you want, or press “Shift+Control+N” to bring up the “Go

To Page” dialog box.

Note: I have intentionally numbered the entire Guide starting with page number

1—as opposed to restarting the page numbers after the Table of Contents and so

forth—so that the Adobe Acrobat page numbers and document page numbers are

identical.

Zooming

By default, The TCP/IP Guide opens up at 100% (actual size) magnification. This provides

the best quality of text and graphics on most monitors, but may not be suitable for some

displays, especially very small or large ones. You can change the displayed size in a variety

of ways. Select a different magnification using the zoom factor drop-down box at the top of

the program, or click one of the pictures of a piece of paper there. To bring up a dialog box

with zoom options, select the “View” menu and then “Zoom To...”, or press “Ctrl+M”. If you

are not sure what magnification to use, try making the Acrobat window full-screen and then

selecting “Fit Width”.

Page Layout

By default, the Guide displays as a continuous scroll of pages, as I find this usually makes

reading a long document easier. It also enables hyperlinks to properly position the

document to the exact location of the target of the link. If you prefer, you can change to

single page layout by selecting the “View” menu, then “Page Layout”, then “Single Page”. If

you do this, however, when you click a hyperlink, it will load the target page number without

scrolling to the title of the hyperlink’s target.

Text Search

To search for a term or phrase, select the “Edit” menu, then “Search”, or press “Ctrl+F”. This

should cause a pane to appear on the right side that presents a few options for you to

search the Guide. A few specific pointers here:

☯ To search for a word or phrase, simply enter it into the box at the top of the search

pane. A results box will come up containing just the single TCP/IP Guide document;

click the “+” next to it for a list of each location in the document where the word or

phrase occurs. Select one and you will be taken directly to it.

☯ To instantly go to the next search result, press “Ctrl+G”; to go to the previous one,

press “Shift+Ctrl+G”. Of course, you can also just select a different result from the box,

rather than moving through each one in sequence.

☯ For more advanced searches, click “Use Advanced Search Options” near the bottom

of the search window.

☯ Click “New Search” to look for a different word or phrase, or use the “Hide” button at

the top right to close the search pane.

☯ The Guide comes with a precompiled index that makes searching through it very fast

despite its size. This index should be automatically loaded when you open the Guide.

Make sure it is selected by checking that under “Where would you like to search?” the

button is next to “In the index named The TCP-IP Guide.pdx”. If you select instead “In

the current PDF document”, the software will search through every page one by one

which will take a long time.

If the index is not present as an option in the search box, try adding it manually. Click “Use

Advanced Search Options” near the bottom of the search pane. Then click the “Look In:”

drop-down box to see if the index is listed. If it is, select it, otherwise, click “Select Index...”.

Then click “Add” and navigate to the location on your computer’s hard disk or CD-ROM

drive where The TCP/IP Guide is located. Select “The TCP-IP Guide.pdx” and it should

attach the index to the document. Then click “Use Basic Search Options” near the bottom of

the window to return to the simpler search box.

Note: If you experience errors when attempting to use the index, this may be due

to an issue with older versions of Adobe Acrobat Reader (even though the PDF

was created to allow compatibility with older software!) Try upgrading to the latest

version of the software; you can download it free from Adobe’s Web site. Sorry for the

inconvenience.

Feedback and Suggestions

One of the ways that this Guide differs from the typical technical reference book is that it is

a very personal work. When you read the material here, I want you to feel like I am

explaining the many technologies and concepts to you personally, because that’s how I feel

when I am writing. A published Guide of this sort is by its nature a type of “one-way”

communication, from me to you; however, I am also interested in what you have to say to

me. For this reason I strongly encourage you to provide me with feedback on this Guide

and suggestions that you may have for it.

On The Web: All technical documents have mistakes in them; this one is no

exception, which is why the Guide is revised regularly. Before contacting me

regarding an error or problem with this Guide, please check to see if you have the

latest version, which may have addressed your concern; the list of versions and the major

changes they contain is at http://www.tcpipguide.com/versions.htm. If you are reading the

current version, please check the errata page, to see if what you found has already been

reported. That page can be found here: http://www.tcpipguide.com/errata.htm

Please Write Me About...

Here, specifically are some of the areas where I would very much like your feedback:

☯ Error Reports: Please don’t be shy about reporting any errors you may find with this

Guide, be they typos, mistakes in my reasoning, glitches in diagrams or anything else.

Simply put, I’m not perfect, and I can’t fix problems that I don’t know exist.

If you do decide to report an error, please check the errata page mentioned above

before contacting me. If your problem is not mentioned there, please e-mail me (see

below) and indicate clearly what version of the Guide you are using, and the topic

name or page number where you found the problem.

☯ Constructive Criticisms and Suggestions for Improvement: If there is something

you don’t like about the material, please tell me. Even better, make a suggestion for

how to improve it.

☯ Requests For Additional Content: Is there an area of the Guide where you wish I

had gone into more detail, or a protocol you feel I should have covered but did not?

Please feel free to let me know.

☯ Compliments: If you like The TCP/IP Guide, then by all means please tell me, I won’t

mind at all! ☺

☯ Questions About The Guide: Questions that pertain directly to the use of the Guide,

its construction, or related matters are fine.

Obviously I cannot guarantee that I will implement every idea or suggestion, but I will

certainly consider each one. I also try to always respond to my e-mail personally, since I

think it is rude for me not to reply when someone takes the time to provide me with

feedback. (I do not, however, usually bother to reply to “flaming” or rude e-mails.)

Please Do Not Write Me About...

The only request I would make is this: please do not contact me with technical

questions or requests for assistance. I’m a pretty busy guy and I get a lot of e-mail. I

simply do not have the time to help people with specific problems. Since I initially wrote my

first project (The PC Guide) in 1997, I have repeatedly asked people not to send me

technical questions, but they keep doing it. I have now had to take the position of simply

ignoring such messages. Specifically, I will not respond to the following:

☯ Requests for network or PC design, setup, configuration or troubleshooting assis-

tance. There are a number of excellent resources for assistance with these types of

issues on the Web, such as The PC Guide Discussion Forums (see below).

☯ Questions from exams, certification practice tests, and so forth. Please do your own

homework, if you want to learn anything at all.

☯ Requests for me to write long treatises about TCP/IP protocols or technologies that go

beyond what this Guide already contains. There’s a lot of detail here, but I obviously

couldn’t include everything that everyone might have wanted to know about. If you

don’t find what you need here, try using another TCP/IP book, or searching the

Internet for the information you need. I am happy to consider requests for enhance-

ments to future versions of the Guide, but I do not have the time for personal

instruction.

On The Web: If you do need help or advice with networking problems or issues, try

The PC Guide Discussion Forums. While many of the discussions there are

oriented specifically around PC hardware and operating system issues, there are

also forums dedicated to networking concerns. You can find them here: http://

www.pcguide.com/forums

My Contact Address

Now that you have read all that—you did read it, didn’t you? ☺—you can reach me through

e-mail at this address: tcpipfb@tcpipguide.com

Version History

Like all technical documents, The TCP/IP Guide must be revised on a regular basis, to

correct problems and make updates to reflect changing technology. The fact that the Guide

is self-published in electronic form allows me to update it much more often than is possible

with a printed book. To differentiate between successive revisions of the Guide, I use a

version number system; you can find the version number of the document you are reading

right now in the footer of each page. I also provide a history of the Guide’s past versions in

this topic, for your reference.

The version number takes the form “N.N”, where each “N” is an integer. The right-most digit

is the minor version number; it is incremented whenever a new version of the Guide is

published that contains only relatively minor fixes and improvements. The left-most digit is

the major version number, and is changed only when significant changes are made to the

Guide, such as a large number of fixes and enhancements, or the addition of substantial

new content.

On The Web: The version history in this topic is obviously only current as of the

date that this particular version of the Guide was published. The most recent list of

versions can be found at http://www.tcpipguide.com/versions.htm. Also, even

though this is an electronic document, a fair bit of work is still required to publish each new

version. Therefore, I do not put out a new version each time a problem is reported to me or

I make a minor enhancement. To see a list of problems or issues that are due to be

corrected in the next version, please check The TCP/IP Guide errata page: http://

www.tcpipguide.com/errata.htm

The version history of The TCP/IP Guide can be found in Table 1.

Table 1: Version History

Version

Number

Version Date Description

1.0 January 1, 2004 Initial release of The TCP/IP Guide.

2.0 June 7, 2004

Extensive rewrite of version 1.0 of The TCP/IP Guide. The Guide was

thoroughly reviewed by two TCP/IP experts and numerous technical

errors and clarity problems were addressed. Most of the larger topics

have had subheaders added to make them more readable. Hundreds of

other minor glitches, typos and problems have also been corrected.

3.0 Sept. 20, 2005

This release contains dozens of technical corrections, grammatical fixes

and other minor improvements. Technically, this might only have been

worthy of a minor upgrade (to version 2.1) but since this version

coincides with the publication of The TCP/IP Guide print book, I decided

to go straight to version 3.0.

Networking Fundamentals

In order to get the most of The TCP/IP Guide, a certain level of knowledge regarding the

basics of networking is very helpful. Unlike many other resources, however, I did not want to

start with the assumption that my reader knew what networking was all about. After all,

that's why you are reading this Guide!

So, I decided to include this section, which provides an overview of some of the basic

issues related to networking. This area is where I place discussions of some of the most

fundamental networking concepts and ideas. It serves not only to provide you, the reader,

with useful background material, but also as a repository for “general” information so that I

don't need to repeat it in many different places elsewhere in the Guide. This in turn allows

those who already know about these basics to avoid having to skip over them in many other

locations.

In this section I have provided several subsections that introduce networking and talk about

some of its most important fundamental concepts. First, I introduce networking in very

broad terms, discussing what it is and why it is important. Then, I describe several funda-

mental characteristics of networks that you will need to understand the various networking

technologies. I discuss the different general types and sizes of networks and how they are

differentiated. I then talk about many different matters related to network performance. I

explain the importance of networking standards and standards organizations. Finally, I

provide a background section that describes the fundamentals of how data is stored and

manipulated in computers; if you are new to computing you may find that information useful

when reading some parts of this Guide.

Note: If you are experienced in networking and related technologies, you may

wish to skip this chapter. Hyperlinks in other areas of the Guide refer back here as

appropriate, so if you need to “fill in” your knowledge of a particular fundamental

“on the fly” you can do so rather easily.

Note: This section discusses fundamental networking issues that may be of use in

understanding certain TCP/IP concepts. However, some of the material is very

broadly oriented towards discussions of networking as a whole and is not specific

to TCP/IP internetworking.

Introduction to Networking

In this day and age, networks are everywhere. The Internet has also revolutionized not only

the computer world, but the lives of millions in a variety of ways even in the “real world”. We

tend to take for granted that computers should be connected together. In fact, these days,

whenever I have two computers in the same room, I have a difficult time not connecting

them together!

Given the ubiquitousness of networking, it's hard to believe that the field is still a relatively

young one, especially when it comes to hooking up small computers like PCs. In

approaching any discussion of networking, it is very useful to take a step back and look at

networking from a high level. What is it, exactly, and why is it now considered so important

that it is assumed that most PCs and other devices should be networked?

In this section, I provide a quick introduction to networking, discussing what it is all about in

general terms. I begin by defining networking in the most general terms. I then place

networking in an overall context by describing some of its advantages and benefits, as well

as some of its disadvantages and costs.

What Is Networking?

For such an extensive and involved subject, which includes so many different technologies,

hardware devices and protocols, the definition of networking is actually quite simple. A

network is simply a collection of computers or other hardware devices that are connected

together, either physically or logically, using special hardware and software, to allow them to

exchange information and cooperate. Networking is the term that describes the processes

involved in designing, implementing, upgrading, managing and otherwise working with

networks and network technologies.

Key Concept: A network is a set of hardware devices connected together, either

physically or logically to allow them to exchange information.

Networks are used for an incredible array of different purposes. In fact, the definitions

above are so simple for the specific reason that networks can be used so broadly, and can

allow such a wide variety of tasks to be accomplished. While most people learning about

networking focus on the interconnection of PCs and other “true” computers, you use various

types of networks every day. Each time you pick up a phone, use a credit card at a store,

get cash from an ATM machine, or even plug in an electrical appliance, you are using some

type of network.

In fact, the definition can even be expanded beyond the world of technology altogether: I'm

sure you've heard the term “networking” used to describe the process of finding an

employer or employee by talking to friends and associates. In this case too, the idea is that

independent units are connected together to share information and cooperate.

The widespread networking of personal computers is a relatively new phenomenon. For the

first decade or so of their existence, PCs were very much “islands unto themselves”, and

were rarely connected together. In the early 1990s, PC networking began to grow in

popularity as businesses realized the advantages that networking could provide. By the late

1990s, networking in homes with two or more PCs started to really take off as well.

This interconnection of small devices represents, in a way, a return to the “good old days” of

mainframe computers. Before computers were small and personal, they were large and

centralized machines that were shared by many users operating remote terminals. While

having all of the computer power in one place had many disadvantages, one benefit was

that all users were connected because they shared the central computer.

Individualized PCs took away that advantage, in favor of the benefits of independence.

Networking attempts to move computing into the middle ground, providing PC users with

the best of both worlds: the independence and flexibility of personal computers, and the

connectivity and resource sharing of mainframes. in fact, networking is today considered so

vital that it’s hard to conceive of an organization with two or more computers that would not

want to connect them together!

The Advantages (Benefits) of Networking

You have undoubtedly heard the “the whole is greater than the sum of its parts”. This

phrase describes networking very well, and explains why it has become so popular. A

network isn't just a bunch of computers with wires running between them. Properly imple-

mented, a network is a system that provides its users with unique capabilities, above and

beyond what the individual machines and their software applications can provide.

Most of the benefits of networking can be divided into two generic categories: connectivity

and sharing. Networks allow computers, and hence their users, to be connected together.

They also allow for the easy sharing of information and resources, and cooperation

between the devices in other ways. Since modern business depends so much on the intel-

ligent flow and management of information, this tells you a lot about why networking is so

valuable.

Here, in no particular order, are some of the specific advantages generally associated with

networking:

☯ Connectivity and Communication: Networks connect computers and the users of

those computers. Individuals within a building or work group can be connected into

local area networks (LANs); LANs in distant locations can be interconnected into

larger wide area networks (WANs). Once connected, it is possible for network users to

communicate with each other using technologies such as electronic mail. This makes

the transmission of business (or non-business) information easier, more efficient and

less expensive than it would be without the network.

☯ Data Sharing: One of the most important uses of networking is to allow the sharing of

data. Before networking was common, an accounting employee who wanted to

prepare a report for her manager would have to produce it on his PC, put it on a floppy

disk, and then walk it over to the manager, who would transfer the data to her PC's

hard disk. (This sort of “shoe-based network” was sometimes sarcastically called a

“sneakernet”.)

True networking allows thousands of employees to share data much more easily and

quickly than this. More so, it makes possible applications that rely on the ability of

many people to access and share the same data, such as databases, group software

development, and much more. Intranets and extranets can be used to distribute

corporate information between sites and to business partners.

☯ Hardware Sharing: Networks facilitate the sharing of hardware devices. For example,

instead of giving each of 10 employees in a department an expensive color printer (or

resorting to the “sneakernet” again), one printer can be placed on the network for

everyone to share.

☯ Internet Access: The Internet is itself an enormous network, so whenever you access

the Internet, you are using a network. The significance of the Internet on modern

society is hard to exaggerate, especially for those of us in technical fields.

☯ Internet Access Sharing: Small computer networks allow multiple users to share a

single Internet connection. Special hardware devices allow the bandwidth of the

connection to be easily allocated to various individuals as they need it, and permit an

organization to purchase one high-speed connection instead of many slower ones.

☯ Data Security and Management: In a business environment, a network allows the

administrators to much better manage the company's critical data. Instead of having

this data spread over dozens or even hundreds of small computers in a haphazard

fashion as their users create it, data can be centralized on shared servers. This makes

it easy for everyone to find the data, makes it possible for the administrators to ensure

that the data is regularly backed up, and also allows for the implementation of security

measures to control who can read or change various pieces of critical information.

☯ Performance Enhancement and Balancing: Under some circumstances, a network

can be used to enhance the overall performance of some applications by distributing

the computation tasks to various computers on the network.

☯ Entertainment: Networks facilitate many types of games and entertainment. The

Internet itself offers many sources of entertainment, of course. In addition, many multi-

player games exist that operate over a local area network. Many home networks are

set up for this reason, and gaming across wide area networks (including the Internet)

has also become quite popular. Of course, if you are running a business and have

easily-amused employees, you might insist that this is really a disadvantage of

networking and not an advantage!

Key Concept: At a high level, networks are advantageous because they allow

computers and people to be connected together, so they can share resources. Some

of the specific benefits of networking include communication, data sharing, Internet

access, data security and management, application performance enhancement, and

entertainment.

Well, if that list isn't enough to convince you that networking is worthwhile, then… I have no

idea what it is you do with your computers! ☺ At any rate, it's quite possible that only some

of the above items will match your particular circumstances, but at least one will definitely

apply to almost every situation, assuming you own or manage more than one computer.

The Disadvantages (Costs) of Networking

Now that I have portrayed the great value and many useful benefits of networking, I must

bring you crashing back to earth with that old nemesis of the realistic: TANSTAAFL. For

those who are not Heinlein fans, this acronym stands for “There Ain’t No Such Thing As A

Free Lunch”. Even though networking really does represent a “whole that is greater than

the sum of its parts”, it does have some real and significant costs and drawbacks

associated with it.

Here are a few of the items that balance against the advantages of networking.

☯ Network Hardware, Software and Setup Costs: Computers don't just magically

network themselves, of course. Setting up a network requires an investment in

hardware and software, as well as funds for planning, designing and implementing the

network. For a home with a small network of two or three PCs, this is relatively

inexpensive, possibly amounting to less than a hundred dollars with today's low prices

for network hardware, and operating systems already designed for networks. For a

large company, cost can easily run into tens of thousands of dollars—or more.

☯ Hardware and Software Management and Administration Costs: In all but the

smallest of implementations, ongoing maintenance and management of the network

requires the care and attention of an IT professional. In a smaller organization that

already has a system administrator, a network may fall within this person's job respon-

sibilities, but it will take time away from other tasks. In more substantial organizations,

a network administrator may need to be hired, and in large companies an entire

department may be necessary.

☯ Undesirable Sharing: With the good comes the bad; while networking allows the

easy sharing of useful information, it also allows the sharing of undesirable data. One

significant “sharing problem” in this regard has to do with viruses, which are easily

spread over networks and the Internet. Mitigating these effects costs more time,

money and administrative effort.