Table Of ContentecaferP
In the developed parts of the world virtually all information-based organiza-
tions are underpinned by some form of communications infrastructure, and
for many companies the communications network si intimately bound with
core business operations. For large, multinational companies the annual
cost of running such an infrastructure may run into millions of dollars, and
the unexpected cost of service outages may be equally sa large. Good net-
work design and attention to detail are fundamental to providing cost-effec-
tive and reliable data networks. It si surprising, therefore, that there are very
few books that deal with the subject of network design from the ground up,
combining the theoretical, practical, and financial issues associated with real
design networks.
Designing modern enterprise networks si now so complex that it cannot
be achieved without the use of specialist software tools, and, sa with any
large problem, it si also beneficial to break down the problem into manage-
able components. There ,si fortunately, a natural split in the design process
between the delivery of the physical topology (be it a local or wide area net-
work) and the routing and higher-layer services. This split mirrors what we
find in the field today. There seem to be two broad classes of network
designer: those who know much about routing and little about topology
analysis, and vice versa. Unfortunately, knowledge of both si critical in plan-
ning and implementing an efficient data network. Network design must be
approached holistically, from the ground up; otherwise, the result si typi-
cally a suboptimal network, with substantial reengineering costs due to
inappropriate assumptions made during the design phase.
Since this is such a huge topic, I have divided my treatment into two
books. In this book we discover how to deliver an optimized logical
topology~covering the addressing, routing, and security issues required
for delivering enterprise services, and how such networks should be
tuned for performance, availability, and maintainability. The first book
xii Preface
ecnamrofreP-hgiH( Data Network )ngiseD deals with the design techniques
required to deliver an optimized physical topology. The book covers the
design process from initiation, capacity planning, backbone and access
design, and performance modeling, to the various LAN, MAN, and WAN
switching technologies required to deliver a basic network infrastructure.
My objective in starting this project was to unite a number of apparently
disparate areas of network design and to provide a balance of theoretical and
practical information that practicing engineers would find useful in their
day-to-day job. Since network design often receives very fragmented cover-
age, this book si an attempt to bring together those pieces so that they may
be seen in context. In particular, the key issues in designing network
addressing schemes are discussed, including how to design using the latest
routing protocols, how to optimize performance using the latest technolo-
gies, how to build fault-tolerant and resilient networks within budget, how
to assess and quantify risk in order to deploy security technologies appropri-
ate for each network, how to deploy Virtual Private Networks (VPNs),
understanding the latest developments in Quality of Service (QoS), and,
finally, how to manage and maintain networks.
I started this project in an environment where the goalposts are far from
static. The speed of change in information technology si simply staggering:
Within the last 20 years we have seen a massive shift from large, centralized,
host-centric networks to a situation where most of today's computing power
reside on desktops. With processing power growing exponentially, and
memory prices declining every year, we are now witnessing another para-
digm shift toward an era of mobile personal computing. We have seen the
emergence of distributed architectures, multimedia, and the explosive
growth of the Internet and the World Wide Web (WWW), each forcing the
development of new protocols and new applications. Network security has
become a real force for change in recent years, with massive growth in the
firewall market and completely new models of secure networking, such sa
the Public Key Infrastructure (PKI) and VPNs. Businesses are now
demanding quality-of-service guarantees and information privacy, and there
si increasing emphasis on Service-Level Agreements (SLAs). With overall
improvements in the communications infrastructure we have also seen a sig-
nificant increase in voice communications, new applications for packetized
Voice over IP (VolP), and the unification of both text and audio messaging
systems. Finally, there are radical changes afoot in the field of user inter-
faces, including the take-up of voice recognition, text to audio translation,
and the use of biometrics.
About this book xiii
In lla areas of technology the boundaries are blurring between local and
wide area networks, data and voice, wired and wireless. All of these technol-
ogies are now being provisioned via a new breed of highly integrated hybrid
devices with built-in routing, switching, bandwidth management, and secu-
rity services. In a very short space of time every home will have Internet
ssecca via smart, integrated digital terminals. There has already been a mas-
sive shift in the adoption of mobile wireless computing and Internet access
via a new generation of data-aware mobile phones. Over the next few years
we will ees the adoption of Java-enabled telephony, with high-resolution
color displays capable of running more powerful applications. This,
together with the use of more intuitive user interfaces and voice recogni-
tion, will truly mobilize the face of personal computing. We can only guess
what changes the next two decades will bring.
About this book
This book si written for practicing engineers and project managers involved
in planning, designing, and maintaining data networks. It si also appropri-
ate for undergraduate students who have taken basic courses in data com-
munications. The content reflects much of my experience in the industry,
having worked for several leading network manufacturers in the areas of
network design, network security, network modeling, and simulation.
This book represents the second of two complementary books on net-
work design and optimization. This book covers addressing and naming
schemes, routing protocols and router design, security techniques, virtual
private networks, network optimization, designing high-availability and
fault-tolerant networks, quality of service, and the management and main-
tenance of networks. The book deals with network design systematically,
assuming that the core LAN, MAN or WAN infrastructure si in place, sa
described in the first book.
Since this book si concerned primarily with large-scale network design,
it focuses heavily on the IP protocol suite, rather than attempting exhaus-
tive coverage of other protocol stacks. Because my primary focus si on the
design and performance characteristics of data networks, the approach
taken throughout this book si to document technologies in sufficient depth
only where they are relevant; for exhaustive information the book cites
numerous good references, including TCP/IP Explained, by Phil Miller,
from Digital Press.
I Preface
xiv Conventions used ni this book
Although the book does include occasional material where numerical
techniques are presented, it si not heavily mathematical. The book also
makes occasional use of programming code, although the reader may skip
these sections. Unfortunately, the use of design algorithms and numerical
modeling si an important part of network design. Where appropriate, suit-
able references are provided.
Conventions used in this book
Throughout the book I use the following format conventions:
(cid:12)9 References are provided at the end of each chapter. Referrals within
the text appear in square brackets 1.
(cid:12)9 Items in angle brackets indicate that the contents of the brackets are
to be replaced by appropriate keywords or data: <netlD><hostlD>.
(cid:12)9 Numbers appear in decimal format unless otherwise indicated. The
prefix 0x si used to indicate hexadecimal numbers (0x6e4d).
stnemgdelwonkcA
As anybody involved in such a large undertaking will attest, attempting to
write such a book without feedback si a recipe for insanity. Therefore, I
must thank a number of individuals for their time and constructive input
on this project. For painstakingly reviewing the content and making
numerous suggestions I have Brian Hill of Xyplex to thank. For reviews and
helpful suggestions on security and routing topics I must thank my col-
leagues Philip Miller, Andrew Namboka, and Bob Brace of Nokia Internet
Communications; Alex Challis of Asita Technologies; and Derin Mellor.
For editing and compiling the final version of this text, I thank Dr. Paul
Fortier and Gurukumar Anantharama Sarma of the University of Massa-
chusetts, Dartmouth. I thank Pam Chester and the folks at Digital Press for
affording me the opportunity to bring this project to life. Finally, I must
thank my wife Amita and my son Jai for their patience and support.
This book does not reflect the policy or the position of any organization
I have worked for. No financial support, resources, or direction was
obtained from these organizations, and the ideas and opinions presented
here (rightly or wrongly) are strictly personal. I apologize for any errors I
have made that may offend or mislead. Please forward any constructive
input to my e-mail address or to Digital Press.
XV
ivx About the Author
About the Author
Tony Kenyon si the Chief Technical Officer of Advisor Technologies Ltd.
(ATL), based in Berkshire, United Kingdom. ATL develops enterprise secu-
rity management solutions for multivendor networks. He was formerly
Technical Director for Europe, the Middle East, and Africa at Nokia Inter-
net Communications and has worked in the data communications industry
since 1983. Tony has designed several international communications net-
works and has developed a number of modeling tools, including an award-
winning graphical object-oriented network design suite. For comments to
the author he can be reached at [email protected].
I
A Review of scisaB eht
Designing an efficient, cost-effective network that meets or exceeds the
requirements si no easy matter. Today's equipment and technologies are
becoming increasingly diverse and have the alarming property of becoming
"old technology" almost sa soon sa they are installed. Mistakes can be, and
often are, expensive. This chapter provides some basic definitions and intro-
duces the concepts of a design process, the intention of which si to ensure
that the design develops in a structured way, with all relevant data exposed
during the process so that there are no late surprises. It resembles Chapter 1
of ecnamrofreP-hgiH Network :ngiseD Design seuqinhceT and slooT 1[ ], and
has been included for the sake of completeness. This chapter also introduces
the basic hardware and software building blocks used in the construction of
modern network designs.
I.I Network design and performance
No two people agree exactly on what network design .si Network design si a
generic and often subjective term that covers a whole range of skills and
tasks, from the logical design elements (such sa network protocols, address-
ing, subnetting), down to the physical design elements (such sa physical
topology, traffic modeling, circuit infrastructure). This book attempts to
provide a holistic approach to network design by covering all the essential
elements from the ground up. Whatever be your particular perspective at
this point in time, by the end of this book you will get an appreciation of
the subject sa a whole.
1.1.1 Elements of good network design
The acid test of a good network design si whether it actually works. The
fact si that many organizations today rely on networks that either perform
2 I. I Network design and performance
suboptimally or cost more than they should, possibly due to poor design or
implementation. These networks can soldier on for years, soaking up more
and more resources and money, until somebody takes a serious look at what
si going on and decides.that things can be improved. The accumulated costs
can be frightening in a badly designed international network, and it is still
not unusual for a preferred supplier to be thrown out of an account after
installation, simply because the proposed design just does not work or the
equipment doesn't do what it was supposed to. Life is still full of surprises in
the networking world, and every new technology appears to bring with it a
new set of implementation issues.
A good network design should have the following characteristics:
(cid:12)9 It should deliver the services requested by its users.
(cid:12)9 It should deliver acceptable throughput and response times.
(cid:12)9 It should be within budget and should maximize cost efficiencies.
(cid:12)9 It should be reliable.
(cid:12)9 It should be expandable without requiring a major redesign.
(cid:12)9 It should be manageable and maintainable by support staff.
(cid:12)9 It should be well documented.
Above all, a network must meet the application and business expecta-
tions of the users; otherwise, it has simply failed to deliver. With today's
increasing shortage of skilled engineers it is also vital that even a well-
designed network is modular, consistent, and well documented. The down-
side of ignoring these issues si that time and money are often wasted debug-
ging problems, things are bolted onto the network in a nonstandard way
(generating more problems), and eventually the business may have to out-
source all management of the network as it becomes just too painful to
administer. The golden rule, therefore, :si Keep it simple.
I.I.2 Network performance
Your job as a network designer, is to understand the complexities of perfor-
mance analysis and then use that knowledge to build a network that satisfies
its users.
In an environment where there is little technical competence it may be
important to first educate the users about what they can reasonably expect
from the network before moving ahead too quickly; this might at times
involve stating the obvious. It is still not uncommon to hear statements
2.1 An overview of the design process 3
such sa "the new network si rubbish, there si absolutely no improvement in
our database tool." For users who were previously using standalone applica-
tions and directly connected printers, installing a fast new network si gener-
ally not going to speed things up, and this can often lead to major
misconceptions.
With any network design we must focus on what typically concerns the
organization most: the performance of the applications and services
accessed by its workers and its clients. For network users the most impor-
tant performance characteristics are those they can directly experience, such
sa response time and delay. However, there are many other aspects of perfor-
mance that are important for optimizing bandwidth and running costs~
factors that may directly impact profitability of productivity for the business
or organization sa a whole.
Characterizing performance, particularly on a large heterogeneous inter-
network, si a complicated task that requires expertise, since there are many
complex interdependencies between systems, protocols, queues, and appli-
cation software.
1.2 An overview of the design process
1.2.1 The life cycle of a design
Network designs are predominantly living entities; they rarely stay the
same. Even from inception to initial implementation, a design will often
change~typically because of improvements in the quality of the data about
the users, applications, and traffic flows, or design changes concerning the
equipment selected and delivery technologies used. The point at which a
network si installed often marks the start of a new phase of design rather
than the end of the process. Consequently, it si useful to think of network
design sa a cyclic process, sa illustrated in Figure 1.1.
Before the design process can begin, a clear set of requirements should
be established to capture what the organization and its users expect from the
network and the services to be offered. The requirements should also clearly
identify what the budget is and any other constraints that impact the
design. The network design process then naturally follows a set sequence:
(cid:12)9 Information gathering
(cid:12)9 Planning
(cid:12)9 Implementation
I Chapter I
4 2.1 An overview of the ngised ssecorp
(cid:12)9 Acceptance
(cid:12)9 Expansion and modification
just sa with any living organism, networks have a limited life span. Over
time networks become increasingly unreliable, inflexible, and unable to
cope with the pressures placed on them. Advances in network technology
and increases in overall traffic levels render most technology obsolete within
a few short years. The lifetime of a network may be extended with the aid of
transplants to vital organs (upgrading routers, links, etc.); however, there
generally comes a point where the network design itself requires a major
overhaul, often resulting in total replacement (at which point the cycle
starts over).
Some networks are destined to age much faster than others. Since net-
works are becoming increasingly inseparable from the organizations they are
built for, a dynamic organization can put severe strain on a design, forcing
radical changes over a much shorter time than a more stable organization.
Massive growth, mergers, acquisitions, downsizing, or radical new ways of
working can all result in a design that si obsolete or inadequate much faster
than anticipated. Networks may even be dismantled and replaced for purely
political reasons; it si not unusual for one company to take over another and
have the absorbed network completely scrapped (this could simply be
