Computer Networks By Hans-Peter Bischof

Computer Networks

By Hans-Peter Bischof

An introduction to the organization and structuring of computer networks.

The following quesions describe what will be covered in this course.

• What is a computer network?
• What can we do with a computer network?

Keywords: (IPethernet)-address, TCP/IP, UDP, router, bridge, socket, rpc, rpcgen, server, client, arp, rarp ...

Protocol Layering
Protocol layering is a common technique to simplify networking designs by dividing them into functional layers, and assigning protocols to perform each layer's task.

For example, it is common to separate the functions of data delivery and connection management into separate layers, and therefore separate protocols. Thus, one protocol is designed to perform data delivery, and another protocol, layered above the first, performs connection management. The data delivery protocol is fairly simple and knows nothing of connection management. The connection management protocol is also fairly simple, since it doesn't need to concern itself with data delivery.

Protocol layering produces simple protocols, each with a few well-defined tasks. These protocols can then be assembled into a useful whole. Individual protocols can also be removed or replaced.
The most important layered protocol designs are the Internet's original DoD model, and the OSI Seven Layer Model. The modern Internet represents a fusion of both models.

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DNS and BIND Third Edition By Cricket Liu & Paul Albitz

DNS and BIND Third Edition

By Cricket Liu & Paul Albitz

You may not know much about the Domain Name System - yet - but whenever you use the Internet, you use DNS. Every time you send electronic mail or surf the World Wide Web, you rely on the Domain Name System.

You see, while you, as a human being, prefer to remember the names of computers, computers like to address each other by number. On an internet, that number is 32 bits long, or between zero and four billion or so.[1] That's easy for a computer to remember, because computers have lots of memory ideal for storing numbers, but it isn't nearly as easy for us humans. Pick ten phone numbers out of the phone book at random, and then try to remember them. Not easy? Now flip to the front of the book and attach random area codes to the phone numbers. That's about how difficult it would be to remember ten arbitrary internet addresses.

[1] And, with IP version 6, it's soon to be a whopping 128 bits long, or between zero and a decimal number with 39 digits.

This is part of the reason we need the Domain Name System. DNS handles mapping between host names, which we humans find convenient, and internet addresses, which computers deal with. In fact, DNS is the standard mechanism on the Internet for advertising and accessing all kinds of information about hosts, not just addresses. And DNS is used by virtually all internetworking software, including electronic mail, remote terminal programs such as telnet, file transfer programs such as ftp, and web browsers such as Netscape Navigator and Microsoft Internet Explorer.

Another important feature of DNS is that it makes host information available all over the Internet. Keeping information about hosts in a formatted file on a single computer only helps users on that computer. DNS provides a means of retrieving information remotely, from anywhere on the network.

More than that, DNS lets you distribute the management of host information among many sites and organizations. You don't need to submit your data to some central site or periodically retrieve copies of the "master" database. You simply make sure your section, called a zone, is up to date on your name servers. Your name servers make your zone's data available to all the other name servers on the network.

Because the database is distributed, the system also needs the ability to locate the data you're looking for by searching a number of possible locations. The Domain Name System gives name servers the intelligence to navigate through the database and find data in any zone.
Of course, DNS does have a few problems. For example, the system allows more than one name server to store data about a zone, for redundancy's sake. But inconsistencies can crop up between copies of the zone data.

But the worst problem with DNS is that despite its widespread use on the Internet, there's really very little documentation about managing and maintaining it. Most administrators on the Internet make do with the documentation their vendors see fit to provide, and with whatever they can glean from following the Internet mailing lists and Usenet newsgroups on the subject.

This lack of documentation means that the understanding of an enormously important internet service - one of the linchpins of today's Internet - is either handed down from administrator to administrator like a closely-guarded family recipe, or relearned repeatedly by isolated programmers and engineers. New administrators of domains suffer through the same mistakes made by countless others.

Our aim with this book is to help remedy this situation. We realize that not all of you have the time or the desire to become DNS experts. Most of you, after all, have plenty to do besides managing a domain or a name server: system administration, network engineering, or software development. It takes an awfully big institution to devote a whole person to DNS. We'll try to give you enough information to allow you to do what you need to do, whether that's running a small domain or managing a multinational monstrosity, tending a single name server or shepherding a hundred of them. Read as much as you need to know now, and come back later if you need to know more.

DNS is a big topic - big enough to require two authors, anyway - but we've tried to present it as sensibly and understandably as possible. The first two chapters give you a good theoretical overview and enough practical information to get by, and later chapters fill in the nitty-gritty details. We provide a roadmap up front, to suggest a path through the book appropriate for your job or interest.

When we talk about actual DNS software, we'll concentrate almost exclusively on BIND, the Berkeley Internet Name Domain software, which is the most popular implementation of the DNS specs (and the one we know best). We've tried to distill our experience in managing and maintaining a domain with BIND into this book - a domain, incidentally, that is one of the largest on the Internet. (We don't mean to brag, but we can use the credibility.) Where possible, we've included the real programs that we use in administration, many of them rewritten into Perl for speed and efficiency.

We hope that this book will help you get acquainted with DNS and BIND if you're just starting out, let you refine your understanding if you're already familiar with them, and provide valuable insight and experience even if you know 'em like the back of your hand.

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Sendmail Desktop Reference First Edition By Bryan Costales and Eric Allman

Sendmail Desktop Reference First Edition

By Bryan Costales and Eric Allman

The sendmail program is a Mail Transport Agent (MTA). It accepts mail from Mail User Agents (MUAs), mail users (humans), and other MTAs. It then delivers that mail to Mail Delivery Agents (MDAs) on the local machine, or transports that mail to another MTA at another machine. The behavior of sendmail is determined by its command line and by commands in its configuration file.

The sendmail program is written and maintained by Eric Allman at sendmail.org. Versions V8.7 and earlier are no longer supported and are no longer considered secure. If you are not currently running V8.8, we recommend you upgrade now. This Desktop Reference covers sendmail version 8.8.5.

This Desktop Reference is a companion to the second edition of the sendmail book by Bryan Costales with Eric Allman, published by O'Reilly & Associates. Section numbers herein reference the section numbers in that book. This is a reference guide only - for detail or tutorial information, refer to the full sendmail book.

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Managing NFS and NIS Second Edition by Hal Stern, Mike Eisler and Ricardo Labiaga

Managing NFS and NIS Second Edition

by Hal Stern, Mike Eisler and Ricardo Labiaga

This book is of interest to system administrators and network managers who are installing or planning new NFS and NIS networks, or debugging and tuning existing networks and servers. It is also aimed at the network user who is interested in the mechanics that hold the network together.

We'll assume that you are familiar with the basics of Unix system administration and TCP/IP networking. Terms that are commonly misused or particular to a discussion will be defined as needed. Where appropriate, an explanation of a low-level phenomenon, such as Ethernet congestion will be provided if it is important to a more general discussion such as NFS performance on a congested network. Models for these phenomena will be drawn from everyday examples rather than their more rigorous mathematical and statistical roots.

This book focuses on the way NFS and NIS work, and how to use them to solve common problems in a distributed computing environment. Because Sun Microsystems developed and continues to innovate NFS and NIS, this book uses Sun's Solaris operating system as the frame of reference. Thus if you are administering NFS on non-Solaris systems, you should use this book in conjunction with your vendor's documentation, since utilities and their options will vary by implementation and release. This book explains what the configuration files and utilities do, and how their options affect performance and system administration issues. By walking through the steps comprising a complex operation or by detailing each step in the debugging process, we hope to shed light on techniques for effective management of distributed computing environments. There are very few absolute constraints or thresholds that are universally applicable, so we refrain from stating them. This book should help you to determine the fair utilization and performance constraints for your network.

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Network Troubleshooting Tools First Edition by Joseph D. Sloan

Network Troubleshooting Tools First Edition

by Joseph D. Sloan

This book is not a general introduction to network troubleshooting. Rather, it is about one aspect of troubleshooting -- information collection. This book is a tutorial introduction to tools and techniques for collecting information about computer networks. It should be particularly useful when dealing with network problems, but the tools and techniques it describes are not limited to troubleshooting. Many can and should be used on a regular basis regardless of whether you are having problems.

Some of the tools I have selected may be a bit surprising to many. I strongly believe that the best approach to troubleshooting is to be proactive, and the tools I discuss reflect this belief. Basically, if you don't understand how your network works before you have problems, you will find it very difficult to diagnose problems when they occur. Many of the tools described here should be used before you have problems. As such, these tools could just as easily be classified as network management or network performance analysis tools.

This book does not attempt to catalog every possible tool. There are simply too many tools already available, and the number is growing too rapidly. Rather, this book focuses on the tools that I believe are the most useful, a collection that should help in dealing with almost any problem you see. I have tried to include pointers to other relevant tools when there wasn't space to discuss them. In many cases, I have described more than one tool for a particular job. It is extremely rare for two tools to have exactly the same features. One tool may be more useful than another, depending on circumstances. And, because of the differences in operating systems, a specific tool may not be available on every system. It is worth knowing the alternatives.

The book is about freely available Unix tools. Many are open source tools covered by GNU- or BSD-style licenses. In selecting tools, my first concern has been availability. I have given the highest priority to the standard Unix utilities. Next in priority are tools available as packages or ports for FreeBSD or Linux. Tools requiring separate compilation or available only as binaries were given a lower priority since these may be available on fewer systems. In some cases, PC-only tools and commercial tools are noted but are not discussed in detail. The bulk of the book is specific to Ethernet and TCP/IP, but the general approach and many of the tools can be used with other technologies.

While this is a book about Unix tools, at the end of most of the chapters I have included a brief section for Microsoft Windows users. These sections are included since even small networks usually include a few computers running Windows. These sections are not, even in the wildest of fantasies, meant to be definitive. They are provided simply as starting points -- a quick overview of what is available.

Finally, this book describes a wide range of tools. Many of these tools are designed to do one thing and are often overlooked because of their simplicity. Others are extremely complex tools or sets of tools. I have not attempted to provide a comprehensive treatment for each tool discussed. Some of these tools can be extremely complex when used to their fullest. Some have manuals and other documentation that easily exceed the size of this book. Most have additional documentation that you will want to retrieve once you begin using them.

My goal is to make you aware of the tools and to provide you with enough information that you can decide which ones may be the most useful to you and in what context so that you can get started using the tools. Each chapter centers on a collection of related tasks or problems and tools useful for dealing with these tasks. The discussion is limited to features that are relevant to the problem being discussed. Consequently, the same tool may be discussed in several places throughout the book.

Please be warned: the suitability or behavior of these tools on your system cannot be guaranteed. While the material in this book is presented in good faith, neither the author nor O'Reilly & Associates makes any explicit or implied warranty as to the behavior or suitability of these tools. We strongly urge you to assess and evaluate these tool as appropriate for your circumstances.

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Network Troubleshooting Tools (O'Reilly System Administration)

Introduction to Data Communications by Eugene Blanchard

Introduction to Data Communications

by Eugene Blanchard

Data Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it. The actual generation of the information is not part of Data Communications nor is the resulting action of the information at the receiver. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process.

In Local Area Networks, we are interested in "connectivity", connecting computers together to share resources. Even though the computers can have different disk operating systems, languages, cabling and locations, they still can communicate to one another and share resources.

The purpose of Data Communications is to provide the rules and regulations that allow computers with different disk operating systems, languages, cabling and locations to share resources. The rules and regulations are called protocols and standards in Data Communications.....

What is a Network? A network can consist of two computers connected together on a desk or it can consist of many Local Area Networks (LANs) connected together to form a Wide Area Network (WAN) across a continent.

The key is that 2 or more computers are connected together by a communication medium and they are sharing resources. The resources can be files, printers, hard-drives or cpu number crunching power.....

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Communication Networks By Sharam Hekmat

Communication Networks

By Sharam Hekmat

This book is concerned with post-computer communication networks and two of its important streams: data communication and telecommunication. Data communication refers to the communication between digital computers, facilitated by computer networks. Telecommunication refers to the primarily human-to-human communication facilitated by the global telephone system. The differences between these two streams are mainly due to historical reasons. Telecommunication is increasingly relying on digital computer technology, and data communication is relying more than ever on telecommunication networks. The two streams are rapidly converging.

Newcomers to this field are often bewildered by the substantial wealth of information already published on the subject. This book is aimed at this group of people. It provides a broad coverage of the key concepts, techniques, and terminology, so as to prepare readers for more advanced discussions. In-depth discussions of technically-involved topics are intentionally avoided in favor of more general concepts. No previous knowledge of networks or programming is assumed.

The structure of the book is as follows. Chapter 1 introduces computer networks and explains some of their elementary concepts. It also introduces the OSI reference model, upon which later chapters are based. Each of Chapters 2-8 describes one of the seven layers of the OSI model in the context of wide area data networks. Chapter 9 looks at local area networks and their applications. Chapter 10 provides an introduction to telecommunication. Chapter 11 builds on earlier chapters by examining ISDN as the merging point of data and voice networks. Chapter 12 looks at the ATM technology and the potential applications that it can support.

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