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Introduction Who Should Read This Book? To the computer semi-literate, the administrator is “the source.” He is the person who knows everything that there is to know about computers and networking. LAN adminis- trators like this reputation and, where novice users are concerned, it is not difficult to maintain. As more and more people begin to see computing as a way of life, however, the knowledge required for the administrator to maintain her reputation for omnipo- tence is increasing at a rapid rate. That’s where this book comes in. It may just be a casual question from a user, regarding something that he saw on his monitor, like “What does IPX stand for, anyway?” It may be a practical complaint, like “Why can’t I print from my Macintosh to the laser printer near my desk, rather than walking all the way over to Marketing, where the Apple printers are?” Given the way in which computing and the Internet has invaded the mainstream media, it may be a guy from Sales, who has a computer at home, stopping by your office, sticking his head in the door and saying, “Hey, what’s the difference between a SLIP and a PPP connection?” Or, worst of all, it may be your boss, telling you that “I want us to be on the Internet by the end of the month.” Whatever the case, there is going to be, at some point, something that you don’t know or that you can’t handle, and when it comes to networking, this book is designed to be the first place for the LAN administrator to go for information. Product manuals give you the “How?” This book is about the “What?” and the “Why?” For instructions on how to install a stand-alone printer on your network, you go to a product manual. You have already made the decisions as to what kind of printer to buy and what kind of network connection you are going to use. This book is designed to help you in making those decisions. Its value comes earlier in the process, when you are asking the most basic questions, like “How can I provide printing services to the greatest number of different clients, with the fewest administration headaches, for the least amount of money?” What Are the Main Objectives of This Book? You may be the new LAN Administrator at a company, faced with a lot of equipment with which you are unfamiliar. This book can help you get up to speed. You may be working for a growing company that wants to expand its computing services around the office, around the building, the country, or the world. This book is the first step, telling Introduction you what is involved in a certain procedure, providing you with information that will be useful in talking to salespeople and evaluating products and pointing you in the right direction for the next step in the process. This is the age of the heterogeneous network. Computers and LANs that may have been installed as separate systems are now being interconnected to provide uniform access to hardware and information resources and to simplify administration and maintenance. A company may be in the process of phasing out their mainframe systems and replacing them with LANs. In the interim, however, the two will have to be connected. The ben- efits of connecting a company’s remote offices and traveling personnel to a central information source are now widely recognized, and the technology has been developed to make this practice logistically and economically feasible. The vast resources of the Internet are rapidly becoming a fixture, not only in offices but in private homes as well. It is very likely that, within five to ten years, Internet connections will be as common as telephones and televisions. To the non-technical corporate management, a LAN administrator is expected to know something about all of these things. Telecommunications, cable installation, electrical engineering, systems analysis, project management, and technical training are just some of the disciplines involved. We’ve come a long way from the time when a person could learn how to use DOS, take a few NetWare courses, and hang out her shingle as a net- work administrator. Unfortunately, in most companies, management has little concep- tion of the true breadth of knowledge required to cover all of these divergent needs. A typical network administrator may know a great deal about some of these disciplines, a little about all of them, or even nothing about any of them, in some cases. For every practitioner, in every profession, there are elements of his field about which he is expected to know but doesn’t. Most are aware of it, and some are even smug about it (I once met a Professor of English Literature who admitted to having never read Hamlet!). The LAN administrator is no different, and the savvy ones are those who have arrived at the point when faced with a subject that they have heard of and should be familiar with, but aren’t, will nod their heads knowingly, promise to look into the situation, and then read up on it at the next opportunity. This is the book that they should turn to first. Will it tell them absolutely everything that they need to know? Of course not. A single work that covered every aspect of modern computer networking would be the size of the Encyclopedia Britannica and would have to be revised at least once a week. The field is growing and developing at an incredibly rapid rate, and a network administrator must continuously expand and update his knowledge in order to remain current. That is why great pains have been taken in this book to cover the latest developments in the net- working industry. You will find information on a great many of the new technologies that are just entering into general use or are soon to be so. We are not talking about speculative possibilities, though, but concrete products and services that exist in the real world and not just on a drawing board. No one can predict whether or not an emerging technology will become a networking standard. That is as much a question about marketing as it is about the technology itself. Keeping current in today’s networking industry consists largely of anticipating new trends and making sensible judgments as to when (or if) it would be safe, practical, and economical to adopt them for use at your network installation. Those who judge wisely, remain employed. Those who don’t, usually end up making a big mess that must be cleaned up by the next administrator. Unfortunately, a good portion of the effort de- voted to the development of an emerging technology is expended on devising ways to convince you that this product or service is the one that you need and that, until you have it, you will never be up to speed with the industry. We hope, in this book, to sepa- rate the publicity from the facts and provide you with more of the latter than the former. What Should You Get Out of This Book? Computer networking, and indeed computing in general, is about communications. To accomplish even the simplest task using a computer, literally dozens of different forms of electronic signaling and communications are used by the various components involved. People speak of this as the digital age and of binary code as the fundamental communi- cations medium for all computers, everywhere. But how do the zeroes and ones get from one place to another? Just as you can telescope in on a video, audio, or textual format to see its binary code, you can zoom in even farther and look at how electrical currents or light pulses are used to make up the binary format. Many people know a lot about computers, but no one person knows everything about them. From the microscopic inner workings of a microprocessor to the sealed environ- ment where magnetic particles store data on the platters of a hard disk drive all the way up to the microwave and satellite technologies used to transmit data between computers located thousands or even millions of miles apart, the variety and complexity of the signaling and communications techniques involved in networking is colossal in scope. You don’t need to know how to design a microprocessor to purchase a computer. You don’t need to know how to build a space shuttle to bounce a signal off of a satellite. Indeed, you probably do both more frequently than you think, without even knowing it. But there may well be times when you want to know something about what goes on within these “transparent” systems. When you are charged with making a decision as to which processor to have in the thousand computers that your company may be purchas- ing this year, it is good to know something more about the subject than you would nor- mally get in a magazine ad or a TV commercial. That’s what this book is for. The more that you know about the inner workings of a com- puter or a network, the more sense can be made from its outside manifestations, and your troubleshooting skills become that much more acute as a result. What Should You Get Out of This Book? Introduction No one is expected to sit down and read a book like this, from cover to cover. It is more likely to be used as a point of reference, a background source that examines most of the tasks that are likely to be asked of a network administrator as well as most of the technol- ogy with which he comes into daily contact. Keeping it handy will help you to field a lot of the user questions that you normally would not be able to answer. And it will let you keep your rep as the “all-knowing network guru” for a little while longer. Part I Understanding Networks 1 Network Background 2 Overview of Network Systems and Services 3 The OSI Model: Bringing Order to Chaos 4 Upgrading to a WAN Understanding Networks I Chapter 1 Network Background Computer networks have grown dramatically in complexity, geographical range and ubiquity over the last few years. This introductory chapter looks at the current state of networking and provides a brief conceptual context for the mass of technical informa- tion contained in the remainder of this book. The Nature of the Network Data traversing the modern global network must run the gauntlet of a wide range of modern communications technology. Each packet is transmitted, bounced, copied, and mangled so often during its brief life that, at times, it seems remarkable that it is deliv- ered at all. Yet, despite its complexity, the modern network is robust and reliable. This is testimony to the rapid pace of developments in communications hardware but perhaps equally as much to the adoption of a consensus approach to design issues by developers. Heterogeneity Modern networks are remarkably heterogeneous. IBM compatibles and Macintoshes rub shoulders with workstations and mainframes; DOS and Windows platforms share data with UNIX and every other operating system; Ethernet and token ring converse with FDDI and ATM; and all of this takes place over a chaotic mixture of physical media. A single network packet might pass through thinnet, twisted-pair, and fiber-optic cables and laser line-of-sight links before being bounced off a satellite to pass through a similar mix of media at the receiving end. Modularity Heterogeneity is made possible by the growing emphasis on modularity in the design of network hardware and software. There was a time when many developers produced net- work environments that used proprietary network software running over proprietary hardware, using a single type of cable. These simple networks were attractive to many consumers who required a simple, out-of-the-box network solution. Inevitably, however, requirements arose that could not be met by a purely proprietary system. For example, the consumers decided to link their network to another different type of network, or they discovered that they needed to share a resource over the network only to find that it was incompatible with their network product. 1 Chapter 1—Network Background The modular approach overcame these difficulties to a large extent. Network products began to focus on a small area of the network landscape. By the late 1980s, instead of having to decide which network to purchase, consumers found themselves making sepa- rate choices for network adapters, cabling systems, interconnection devices, network operating systems (NOSs), and network applications. Increasing modularity in network software has had an especially profound impact. This is particularly apparent on the desktop, where network protocols can be mixed and matched to suit the user’s needs. Modularity’s effects are becoming increasingly marked on a more macroscopic level, as network administrators combine NOSs to provide the required combination of services rather than rely on a single product. Standards The modular approach is possible only when adequate standards are agreed upon. No- body can predict exactly what a user is going to want to send over the network, nor can anyone know with certainty what the next stage of development in network technology will bring. The only way a developer can be sure that its product will work with the rest of the network is by adhering rigorously to the recognized standards. Each hardware manufacturer must know exactly what it can expect as input to its part of system and what its system must generate as output. Software developers work to similar specifications. The OSI network model discussed in chapter 3, “The OSI Model: Bringing Order to Chaos,” has been extremely influential in this regard, allowing for a clear, logical delin- eation of responsibilities between the many components of a network. At the desktop level, Novell’s ODI specification has allowed what would previously have been unimag- inable—several different network protocols running simultaneously and smoothly on the same hardware. In both cases, the adoption of a standard has made development possible. The Scope of Networking The rapid growth in the number of networked computers over the last decade or so has been dramatic. One index of this growth is the number of Internet host computers, which is now in excess of six million. Figure 1.1 depicts the increase over several years to mid-1995, using data produced by Network Wizards and available on http:// www.nw.com/. The number of people with Internet access is extremely difficult to quantify but is currently in excess of twenty million worldwide. Estimates in the growth of Internet connections, while difficult, are at least possible be- cause of the integrated nature of the Internet. The growth in enterprise-level computing is similarly dramatic but impossible to measure in the same way, as many LANs are iso- lated from the world beyond the enterprise. Understanding Networks I Figure 1.1 This is the growth of Internet hosts from 1988 to 1995. Growth Rate A remarkable feature of this expansion is that the rate of growth has continued to in- crease over a period of years, which has led to predictions of one Internet node for every human being in the planet by the early years of the next century. This acceleration in growth rate is because when two networks are connected, both are expanded and en- hanced. Connecting thousands of LANs made the combined resources of the Internet so vast that it eventually became unrealistic for network planners to attempt to rival it; better to connect to it, take advantage of it, and at the same time, contribute to it. This exponential growth cannot continue indefinitely but by the time it begins to slow, it is likely that Internet access will be as commonplace as cable television. Networks in the home may have seemed unlikely a few years ago, yet some homes have already been fitted with network cabling. The emergence of cost-effective broadband technologies such as ISDN suggests that domestic network access at speeds is not far away. Network Awareness In tandem with this rapid growth in the extent of networks in general and the Internet in particular, there has been a significant change in the general level of awareness of networks. Most computer literate people have by now at least heard of the Internet; many who are not otherwise familiar with computers have also heard of it. In fact, a substantial number of people are now buying their first computer for the purpose of accessing the Internet. Access to the network has become an end in itself. This heightened awareness of networking has been fueled by the rapid expansion of networks into everyday life, which has in turn fueled the heightened awareness of net- working. Networking the office is no longer a matter of office equipment, the impact of which can be compared with the arrival of a new fax machine. Instead, it brings a fundamental change in the way the enterprise functions internally—in the relationship between the enterprise and the world outside and in the staff’s perception of their rela- tionship to the world beyond the office. There is now an increasing awareness within organizations that networking can make this type of change. 1988 1 2 3 4 5 6 0 1989 1990 1991 1992 1993 1994 1995 7 The Scope of Networking Chapter 1—Network Background Network Readiness Application software has been tracking this shift in awareness for some time. Not so many years ago, many applications would balk at working in a networked environment; how many packages refused to use drive letters beyond E? Yet today, more and more packages are claiming to be “network ready” or “network aware” as software developers increasingly recognize networked computers as the norm rather than the exception. Recent developments in software monitoring and license enforcement as described in appendix D, “Software License Metering,” reflect this change. Technology The technological innovations that have driven these changes are not as extensive as may be imagined. Most of the building blocks of the modern network—data packets, protocols, cabling systems—were invented by Rank Xerox in the 1970s. While the speed and capacity of network hardware have developed enormously in recent years, and while today’s networks are built with increasingly sophisticated components, there has been nothing like the paradigm shift introduced by the invention of, say, the transistor. Today’s Networks The rapid pace of change in network hardware and software is reflected in the range of systems in use across the world at the present time. Most network installations, particu- larly those in the medium and large categories, consist of a mixture of old and new hard- ware and software. Legacy Systems Some of the most out-of-date network equipment is found at some of the most progres- sive institutions. These were the pioneers, the ones who invested in early systems at a time when networking was still experimental. They had to struggle with relatively primi- tive equipment and endure frequent crashes and network hiccups, only to find that their system was obsolete almost as soon as it was stable. They then faced a dilemma. Should they write off the old equipment to experience and graduate to a better system, incurring high capital and manpower costs? Or did it make more sense to stick with the old system, enhancing it where possible and hoping to switch at some point in the future? In many cases, the scale of investment required to change was too high. As a result, the existing systems were retained after they had ceased to be worth the maintenance effort. New equipment was brought in on a piecemeal basis to shore up the creaking system until, finally, something gave and the required invest- ment was made. This reluctance or inability to move on to more modern systems has left a considerable amount of old equipment in use. The new products are faster, more modular, and more robust, but most network administrators have to support at least some software and hardware that they would rather see scrapped. Understanding Networks I The Modern Network The modular nature of modern network products and the lessons learned about invest- ment and obsolescence have helped to make recent networks more manageable. They are designed with a view to the finite life span of the components. Obsolescence is planned rather than being allowed to creep up, and the initial investment is made with the un- derstanding that substantial ongoing resources, both monetary and human, will be re- quired to maintain the network as a functioning entity. There is a realization that no matter what capacity is provided, the users will almost certainly exhaust it within a matter of months. Hardware. Computers bought for network access are most likely to be IBM-compatible PCs, Macintoshes, and UNIX systems, in that order. Apple in the past relied on superior technical innovation, particularly in the network arena; this having failed, Apple has now staked a good deal on its PowerPC. As yet, this has not made a significant impact. Many of the computers connected to networks around the world were of course bought before any network was available. These legacy systems will be around for the foreseeable future, and they form a significant part of most network communities. They make their presence felt by being less powerful and less well integrated into the network than their more modern cousins. Software. The software products of the past are much less likely to feature on today’s networks. LocalTalk, LAN Manager, and many others have faded from prominence over a short period of time. Once such products began to be seen as having lost the battle for market preeminence, their demise accelerated as consumers began to back the winners with a vengeance. Those leaders in the desktop market are Novell NetWare for client-server systems and Microsoft Windows (Windows for Workgroups and Windows 95) for peer-to-peer sys- tems. Both are primarily PC-based, reflecting Apple’s slip from the top of the desktop machine market. Larger systems are almost universally TCP/IP based, as in fact are a significant number of smaller systems. Networking. The bulk of new LANs are Ethernet based. Fiber-optic links between build- ings are now the norm, with leased telecommunications lines taking the place of the public data network for wide area links. LANs that are strictly local make less and less sense. Electronic mail has become the sine qua non of network access; this requires a gateway machine of some description and a connection to the world outside. Internet access may have already replaced e-mail in this regard, despite the higher demands it places on bandwidth and other expensive resources. The Future In such a rapidly changing field as computer networking, trying to predict the future is almost certainly an act of folly. If the author could be certain that his predictions were accurate, he would be implementing them rather than merely speculating about them! However, a number of trends appear to be clear. Today’s Networks Chapter 1—Network Background Desktop hardware and software products are increasingly being seen as consumer goods. They have left the realm of specialist retailers and entered the mainstream of office equipment and home appliances. This shift, partly driven by the growth in networking, will itself continue to fuel the demand for network access and for better and faster net- work services. This shift will also accelerate the change in the typical profile of a network user. Aca- demic institutions will soon cease to be the core of the international network commu- nity, and office workers will no longer represent the bulk of LAN users. Instead, domestic network access will rank with professional use in terms of numbers and traffic. The net- work may not become as ubiquitous as the telephone, but it will become much more commonplace than at present. Just as with telephones, the continuing advances in telecommunications will help to make networking more mobile. Laptop and pocket PCs will claim their stake in the cellu- lar communications world and, through sheer weight of traffic, will play a significant part in shaping the successor to the current cellular technology. The trend away from public data networks may well reverse as network providers pro- duce more secure and cost-effective solutions. Utility companies would like to see a move toward complete network packages, where the provider bundles a physical link with gateway and domain management services. Whether they can persuade the network management to go for this depends on design issues on which the jury is still most definitely out. Summary Technological advances in networking hardware and software have led to greater throughput on all scales and to increasingly tighter integration of networking with all aspects of computing. In tandem with these advances, the idea of networking has en- tered the common consciousness to an extent that would have been unimaginable a few short years ago. This shift in perception has led to an expansion of networking beyond the workplace, which is already beginning to shape developments in networking technology. Understanding Networks I2 Chapter 2 Overview of Network Systems and Services A network is an interconnected system of computing devices that provide shared, eco- nomical access to computer services. The task of managing the access to shared services is given to a specialized type of software known as a network operating system (NOS). There are many NOSs available in the marketplace today—the major players are covered in detail in part III, “Software Platforms: NOSs and Clients.” This chapter provides a high- level view of the two main types of local area networks (LAN): client/server and peer-to- peer. It also examines the basic hardware structure that comprises the modern LAN, and looks at some of the features and services furnished by this combination of networking hardware and software. In the process, a good many of the basic networking terms and concepts used throughout this book will also be introduced. The Client/Server Network Client/server computing is a buzzword that has been bandied about a great deal in the computer press, often without being specifically defined. Basically, the client/server con- cept describes a computing system in which the actual processing needed to complete a particular task is divided between a centralized host computer, the server, and a user’s individual workstation, the client. The two are connected by cables (or infrared, radio, or microwaves) for communication (see fig. 2.1). (Note that the connecting lines in the figure represent the network’s pattern of data traffic and not the physical cabling system). Although they are both PCs with the same basic architecture, the client and server com- puters usually have very different hardware and software configurations. The primary function of each in relation to the other can be stated in simple terms: the client requests services from the server, and the server responds by providing those services. A few ex- amples of client/server operations might make this distinction clear: Chapter 2—Overview of Network Systems and Services Workstation (Client) Workstation (Client) Workstation (Client) Server Figure 2.1 This is the logical architecture of a typical client/server network. I A computer running DOS, requesting a file that is stored on a NetWare file server I A PC running Windows 95, dialing out to a bulletin board using a modem con- nected to a RISC-based computer running Windows NT Advanced Server I A Windows application on a user’s PC, requesting data from a computer running Lotus Notes I A PC running DOS and Sun’s PC-NFS product, printing a large report using a high- speed printer attached to a SparcServer I A computer running OS/2, connected to a mainframe, receiving up-to-the-minute data about commodity prices, and displaying a constantly updated chart reflecting the price changes I An Apple Macintosh Performa being used for photo-retouching of a high- resolution scanned image from a Scitex publishing system I A PC, connected to the Internet, running Netscape Navigator and viewing multi- media documents stored on a UNIX host on another continent In each case, it is clear which system is the client and which is the server. It is also clear that the computer operating as the server is providing a service to the client that is essen- tial to complete the task at hand. Indeed, the server could be providing these services to dozens or even hundreds of clients simultaneously. It is not surprising, therefore, that a server is generally a more powerful, complex, and expensive machine—running more powerful, complex, and expensive software—than the clients with which it interacts. The differences in function and ability between the server and the client are in accor- dance with the reasons that PC networks were originally developed and have been so Understanding Networks I The Client/Server Network successful: to provide shared, economical access to services such as large disk drives, high-quality printers, high-speed modems, and other expensive items. Concentrating the most expensive and important pieces of the network at a server allows those items to be protected and maintained by trained professionals, while allowing many more people to use them. This centralized location of shared equipment is, of course, nothing new to computing. It is the essence of the host-based system, in which a mainframe holds all of the data and runs all of the applications, and users interact with the host using terminals to input data and view results. Clearly, another aspect is necessary for a system to be considered a client/server network, and that is the distributed processing previously mentioned. In a host-based system, all the important processing happens on the mainframe. The applica- tion running on the mainframe even controls most of the functions of the users’ termi- nals, telling them where to display certain characters, when to beep and for how long, and when to accept user input. In a client/server relationship, the server does some of the necessary data processing, and the client does some. The degree to which the processing tasks are separated between the two machines can vary greatly, and this is the source of confusion to many. When a user launches an application at his workstation, it may be a spreadsheet whose software is stored and operated solely within the workstation computer, or it may be a database client that interacts with a server to bring information to that workstation. If the data file being opened by the spreadsheet is stored on a network file server, both of these in- stances can, by strict definition, be called client/server applications. Server processes are needed to provide both the spreadsheet and the database with the data files that they need to operate. However, there is a question of degree here that cannot be overlooked. Once the file server has delivered the spreadsheet’s data file to the workstation, its participation in the process is ended, until it is time to write the modified file back to the server. The data- base application, on the other hand, requires the continuous participation of both sides of the client/server paradigm to function. The database client is useless (and sometimes cannot even be launched) unless the server process is active. This is what is really meant by client/server computing. Instead of the entire functional- ity for multiple users being carried out by a single computer, as in the mini/mainframe situation, the processing capabilities of the server and all of the client machines are com- bined into a whole that is inherently more efficient. This is because of reductions in the amount of data being transmitted over the network, as well as the combined increase in pure computing power. There are several types of systems that can be considered servers in a client/server envi- ronment. At the most basic level is a file server that performs high-performance data stor- age duty for multiple clients, and perhaps provides shared print services as well. There can also be large application servers, running high volume applications—such as database access, updating, indexing, selection, and retrieval—on behalf of less powerful clients. Smaller, special-purpose servers may provide fax services, electronic mail pickup and deliv- ery, or modem sharing.
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