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Network Warrior
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Network Warrior
Gary A. Donahue
Beijing
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Network Warrior
by Gary A. Donahue
Copyright © 2007 O’Reilly Media, Inc. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.
O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions
are also available for most titles (safari.oreilly.com). For more information, contact our

corporate/institutional sales department: (800) 998-9938 or
Editor:
Mike Loukides
Production Editor:
Sumita Mukherji
Copyeditor:
Rachel Head
Proofreader:
Sumita Mukherji
Indexer:
Ellen Troutman
Cover Designer:
Karen Montgomery
Interior Designer:
David Futato
Illustrators:
Robert Romano and Jessamyn Read
Printing History:
June 2007: First Edition.
Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of
O’Reilly Media, Inc. The Cookbook series designations, Network Warrior, the image of a German
boarhound, and related trade dress are trademarks of O’Reilly Media, Inc.
Many of the designations used by manufacturers and sellers to distinguish their products are claimed as
trademarks. Where those designations appear in this book, and O’Reilly Media, Inc. was aware of a
trademark claim, the designations have been printed in caps or initial caps.
While every precaution has been taken in the preparation of this book, the publisher and author assume
no responsibility for errors or omissions, or for damages resulting from the use of the information
contained herein.
This book uses RepKover
™

, a durable and flexible lay-flat binding.
ISBN-10: 0-596-10151-1
ISBN-13: 978-0-596-10151-0
[C]
For my girls:
Lauren, Meghan, and Colleen,
and Cozy and Daisy.
—Gary A. Donahue
vii
Table of Contents
Preface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xv
Part I. Hubs, Switches, and Switching
1. What Is a Network?
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2. Hubs and Switches
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
Hubs 6
Switches 10
3. Auto-Negotiation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
What Is Auto-Negotiation? 19
How Auto-Negotiation Works 20
When Auto-Negotiation Fails 20
Auto-Negotiation Best Practices 22

Configuring Auto-Negotiation 23
4. VLANs
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
Connecting VLANs 24
Configuring VLANs 27
5. Trunking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
How Trunks Work 34
Configuring Trunks 38
viii | Table of Contents
6. VLAN Trunking Protocol
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
VTP Pruning 46
Dangers of VTP 47
Configuring VTP 49
7. EtherChannel
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
55
Load Balancing 56
Configuring and Managing EtherChannel 60
8. Spanning Tree
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
66
Broadcast Storms 67
MAC Address Table Instability 72
Preventing Loops with Spanning Tree 73
Managing Spanning Tree 77

Additional Spanning Tree Features 80
Common Spanning Tree Problems 84
Designing to Prevent Spanning Tree Problems 87
Part II. Routers and Routing
9. Routing and Routers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
Routing Tables 92
Route Types 95
The IP Routing Table 95
10. Routing Protocols
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
102
Communication Between Routers 103
Metrics and Protocol Types 106
Administrative Distance 108
Specific Routing Protocols 110
11. Redistribution
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
130
Redistributing into RIP 132
Redistributing into EIGRP 135
Redistributing into OSPF 137
Mutual Redistribution 139
Redistribution Loops 140
Limiting Redistribution 142
Table of Contents | ix
12. Tunnels
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
150

GRE Tunnels 151
GRE Tunnels and Routing Protocols 156
GRE and Access Lists 161
13. Resilient Ethernet
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
163
HSRP 163
HSRP Interface Tracking 166
When HSRP Isn’t Enough 168
14. Route Maps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
172
Building a Route Map 173
Policy-Routing Example 175
15. Switching Algorithms in Cisco Routers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
181
Process Switching 183
Interrupt Context Switching 184
Configuring and Managing Switching Paths 190
Part III. Multilayer Switches
16. Multilayer Switches
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
197
Configuring SVIs 198
Multilayer Switch Models 203
17. Cisco 6500 Multilayer Switches
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
204
Architecture 206

CatOS Versus IOS 222
18. Catalyst 3750 Features
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
227
Stacking 227
Interface Ranges 228
Macros 229
Flex Links 233
Storm Control 233
Port Security 238
SPAN 241
Voice VLAN 244
QoS 247
x | Table of Contents
Part IV. Telecom
19. Telecom Nomenclature
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
253
Introduction and History 253
Telecom Glossary 254
20. T1
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
268
Understanding T1 Duplex 268
Types of T1 269
Encoding 270
Framing 272
Performance Monitoring 274
Alarms 276
Troubleshooting T1s 279

Configuring T1s 283
21. DS3
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
288
Framing 288
Line Coding 292
Configuring DS3s 292
22. Frame Relay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
299
Ordering Frame-Relay Service 302
Frame-Relay Network Design 303
Oversubscription 306
Local Management Interface (LMI) 307
Configuring Frame Relay 309
Troubleshooting Frame Relay 316
Part V. Security and Firewalls
23. Access Lists
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
323
Designing Access Lists 323
ACLs in Multilayer Switches 334
Reflexive Access Lists 338
Table of Contents | xi
24. Authentication in Cisco Devices
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
343
Basic (Non-AAA) Authentication 343
AAA Authentication 353
25. Firewall Theory

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
361
Best Practices 361
The DMZ 363
Alternate Designs 367
26. PIX Firewall Configuration
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
369
Interfaces and Priorities 369
Names 371
Object Groups 372
Fixups 375
Failover 377
NAT 383
Miscellaneous 388
Troubleshooting 391
Part VI. Server Load Balancing
27. Server Load-Balancing Technology
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
395
Types of Load Balancing 396
How Server Load Balancing Works 398
Configuring Server Load Balancing 399
28. Content Switch Modules in Action
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
405
Common Tasks 407
Upgrading the CSM 411
Part VII. Quality of Service
29. Introduction to QoS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
417
Types of QoS 421
QoS Mechanics 422
Common QoS Misconceptions 427
xii | Table of Contents
30. Designing a QoS Scheme
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
430
Determining Requirements 430
Configuring the Routers 435
31. The Congested Network
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
440
Determining Whether the Network Is Congested 440
Resolving the Problem 445
32. The Converged Network
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
447
Configuration 447
Monitoring QoS 449
Troubleshooting a Converged Network 452
Part VIII. Designing Networks
33. Designing Networks
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
461
Documentation 461
Naming Conventions for Devices 472
Network Designs 473
34. IP Design

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
484
Public Versus Private IP Space 484
VLSM 487
CIDR 490
Allocating IP Network Space 491
Allocating IP Subnets 494
IP Subnetting Made Easy 498
35. Network Time Protocol
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
506
What Is Accurate Time? 506
NTP Design 508
Configuring NTP 510
36. Failures
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
513
Human Error 513
Multiple Component Failure 514
Disaster Chains 515
No Failover Testing 516
Troubleshooting 516
Table of Contents | xiii
37. GAD’s Maxims
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
521
Maxim #1 521
Maxim #2 524
Maxim #3 525
38. Avoiding Frustration

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
529
Why Everything Is Messed Up 529
How to Sell Your Ideas to Management 532
When to Upgrade and Why 536
Why Change Control Is Your Friend 539
How Not to Be a Computer Jerk 541
Index
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
545
xv
Preface1
The examples used in this book are taken from my own experiences, as well as from
the experiences of those with or for whom I have had the pleasure of working. Of
course, for obvious legal and honorable reasons, the exact details and any information
that might reveal the identities of the other parties involved have been changed.
Cisco equipment is used for the examples within this book, and, with very few
exceptions, the examples are TCP/IP-based. You may argue that a book of this type
should include examples using different protocols and equipment from a variety of
vendors, and, to a degree, that argument is valid. However, a book that aims to cover
the breadth of technologies contained herein, while also attempting to show exam-
ples of these technologies from the point of view of different vendors, would be
quite an impractical size.
The fact is that Cisco Systems (much to the chagrin of its competitors, I’m sure) is
the premier player in the networking arena. Likewise, TCP/IP is the protocol of the
Internet, and the protocol used by most networked devices. Is it the best protocol for
the job? Perhaps not, but it is the protocol in use today, so it’s what I’ve used in all
my examples. Not long ago, the Cisco CCIE exam still included Token Ring Source
Route Bridging, AppleTalk, and IPX. Those days are gone, however, indicating that

even Cisco understands that TCP/IP is where everyone is heading.
WAN technology can include everything from dial-up modems (which, thankfully,
are becoming quite rare in metropolitan areas) to ISDN, T1, DS3, SONET, and so
on. We will cover many of these topics, but we will not delve too deeply into them,
for they are the subject of entire books unto themselves—some of which may already
sit next to this one on your O’Reilly bookshelf.
Again, all the examples used in this book are drawn from real experiences, most of
which I faced myself during my career as a networking engineer, consultant,
manager, and director. I have run my own company, and have had the pleasure of
working with some of the best people in the industry, and the solutions presented in
these chapters are those my teams and I discovered or learned about in the process of
resolving the issues we encountered.
xvi
|
Preface
Who Should Read This Book
This book is intended for use by anyone with first-level certification knowledge of
data networking. Anyone with a CCNA or equivalent (or greater) knowledge should
benefit from this book. My goal in writing Network Warrior is to explain complex
ideas in an easy-to-understand manner. While the book contains introductions to
many topics, you can also consider it as a reference for executing common tasks
related to those topics. I am a teacher at heart, and this book allows me to teach
more people than I’d ever thought possible. I hope you will find the discussions I
have included both informative and enjoyable.
I have noticed over the years that people in the computer, networking, and telecom
industries are often misinformed about the basics of these disciplines. I believe that
in many cases, this is the result of poor teaching, or the use of reference material that
does not convey complex concepts well. With this book, I hope to show people how
easy some of these concepts are. Of course, as I like to say, “It’s easy when you know
how,” so I have tried very hard to help anyone who picks up my book understand

the ideas contained herein.
If you are reading this, my guess is that you would like to know more about network-
ing. So would I! Learning should be a never-ending adventure, and I am honored
that you have let me be a part of your journey. I have been studying and learning
about computers, networking, and telecom for the last 24 years, and my journey will
never end.
This book attempts to teach you what you need to know in the real world. When
should you choose a layer-3 switch over a layer-2 switch? How do you tell if your
network is performing as it should? How do you fix a broadcast storm? How do you
know you’re having one? How do you know you have a spanning-tree loop, and how
do you fix it? What is a T1, or a DS3 for that matter? How do they work? In this
book, you’ll find the answers to all of these questions, and many, many more. Net-
work Warrior includes configuration examples from real-world events and designs,
and is littered with anecdotes from my time in the field—I hope you enjoy them.
Conventions Used in This Book
The following typographical conventions are used in this book:
Italic
Used for new terms where they are defined, for emphasis, and for URLs
Constant width
Used for commands, output from devices as it is seen on the screen, and samples
of Request for Comments (RFC) documents reproduced in the text
Constant width italic
Used to indicate arguments within commands for which you should supply values
Preface
|
xvii
Constant width bold
Used for commands to be entered by the user and to highlight sections of output
from a device that have been referenced in the text or are significant in some way
Indicates a tip, suggestion, or general note

Indicates a warning or caution
Using Code Examples
This book is here to help you get your job done. In general, you may use the code in
this book in your programs and documentation. You do not need to contact us for
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We appreciate, but do not require, attribution. An attribution usually includes the
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Preface
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Acknowledgments
Writing a book is hard work—far harder than I ever imagined. Though I spent
countless hours alone in front of a keyboard, I could not have accomplished the task
without the help of many others.
I would like to thank my lovely wife, Lauren, for being patient, loving, and support-
ive. Lauren, being my in-house proofreader, was also the first line of defense against
grammatical snafus. Many of the chapters no doubt bored her to tears, but I know
she enjoyed at least a few. Thank you for helping me achieve this goal in my life.
I would like to thank Meghan and Colleen for trying to understand that when I was
writing, I couldn’t play. I hope I’ve helped instill in you a sense of perseverance by
completing this book. If not, you can be sure that I’ll use it as an example for the rest
of your lives. I love you both “bigger than the universe” bunches.
I would like to thank my mother—because she’s my mom, and because she never
gave up on me, always believed in me, and always helped me even when she
shouldn’t have (Hi, Mom!).
I would like to thank my father for being tough on me when he needed to be, for
teaching me how to think logically, and for making me appreciate the beauty in the
details. I have fond memories of the two of us sitting in front of my Radio Shack
Model III computer while we entered basic programs from a magazine. I am where I

am today largely because of your influence, direction, and teachings. You made me
the man I am today. Thank you, Papa. I miss you.
Preface
|
xix
I would like to thank my Cozy, my faithful Newfoundland dog who was tragically
put to sleep in my arms so she would no longer have to suffer the pains of cancer.
Her body failed while I was writing this book, and if not for her, I probably would
not be published today. Her death caused me great grief, which I assuaged by writ-
ing. I miss you my Cozy—may you run pain free at the rainbow bridge until we meet
again.
I would like to thank Matt Maslowski for letting me use the equipment in his lab that
was lacking in mine, and for helping me with Cisco questions when I wasn’t sure of
myself. I can’t think of anyone I would trust more to help me with networking topics.
Thanks, buddy.
I would like to thank Adam Levin for answering my many Solaris questions, even the
really nutty ones. Sorry the book isn’t any shorter.
I would like to thank Jeff Cartwright for giving me my first exciting job at an ISP and for
teaching me damn-near everything I know about telecom. I still remember being taught
about one’s density while Jeff drove us down Interstate 80, scribbling waveforms on a
pad on his knee while I tried not to be visibly frightened. Thanks also for proofreading
some of my telecom chapters. There is no one I would trust more to do so.
I would like to thank Mike Stevens for help with readability and for some of the more
colorful memories that have been included in this book. His help with PIX firewalls
was instrumental to the completion of those chapters.
I would like to thank Peter Martin for helping me with some subjects in the lab for
which I had no previous experience. And I’d like to extend an extra thank you for
your aid as one of the tech reviewers for Network Warrior—your comments were
always spot-on, and your efforts made this a better book.
I would like to thank another tech reviewer, Yves Eynard: you caught some mistakes

that floored me, and I appreciate the time you spent reviewing. This is a better book
for your efforts.
I would like to thank Paul John for letting me use the lab while he was using it for his
CCIE studies.
I would like to thank Henri Tohme and Lou Marchese for understanding my need to
finish this book, and for accommodating me within the limits placed upon them.
I would like to thank Sal Conde and Ed Hom for access to 6509E switches and
modules.
I would like to thank Christopher Leong for doing some last-minute technical
reviews on a couple of the telecom chapters.
I would like to thank Mike Loukides, my editor, for not cutting me any slack, for not
giving up on me, and for giving me my chance in the first place. You have helped me
become a better writer, and I cannot thank you enough.
xx
|
Preface
I would like to thank Rachel Head, the copyeditor who made this a much more
readable book.
I would like to thank Robert Romano, senior technical illustrator at O’Reilly, for work-
ing to keep the illustrations in this book as close to my original drawings as possible.
I would like to thank all the wonderful people at O’Reilly. Writing this book was an
awesome experience, due in large part to the people I worked with at O’Reilly.
I would like to thank my good friend, John Tocado, who once told me, “If you want
to write, then write!” This book is proof that you can change someone’s life with a
single sentence. You’ll argue that I changed my own life, and that’s fine, but you’d be
wrong. When I was overwhelmed with the amount of remaining work to be done, I
seriously considered giving up. Your words are the reason I did not. Thank you.
I cannot begin to thank everyone else who has given me encouragement. Living and
working with a writer must, at times, be maddening. Under the burden of deadlines,
I’ve no doubt been cranky, annoying, and frustrating, for which I apologize.

My purpose for the last year has been the completion of this book. All other respon-
sibilities, with the exception of health and family, took a back seat to my goal.
Realizing this book’s publication is a dream come true for me. You may have dreams
yourself, for which I can offer only this one bit of advice: work toward your goals,
and you will realize them. It really is that simple.
PART I
I. Hubs, Switches, and Switching
This section begins with a brief introduction to networks. It then moves on to describe
the benefits and drawbacks of hubs and switches in Ethernet networks. Finally, many
of the protocols commonly used in a switched environment are covered.
This section is composed of the following chapters:
Chapter 1, What Is a Network?
Chapter 2, Hubs and Switches
Chapter 3, Auto-Negotiation
Chapter 4, VLANs
Chapter 5, Trunking
Chapter 6, VLAN Trunking Protocol
Chapter 7, EtherChannel
Chapter 8, Spanning Tree
3
Chapter 1
CHAPTER 1
What Is a Network?2
Before we get started, I would like to define some terms and set some ground rules.
For the purposes of this book (and your professional life, I hope), a computer net-
work can be defined as “two or more computers connected by some means through
which they are capable of sharing information.” Don’t bother looking for that in an
RFC because I just made it up, but it suits our needs just fine.
There are many types of networks: Local Area Networks (LANs), Wide Area Net-

works (WANs), Metropolitan Area Networks (MANs), Campus Area Networks
(CANs), Ethernet networks, Token Ring networks, Fiber Distributed Data Interface
(FDDI) networks, Asynchronous Transfer Mode (ATM) networks, frame-relay
networks, T1 networks, DS3 networks, bridged networks, routed networks, and
point-to-point networks, to name a few. If you’re old enough to remember the pro-
gram Laplink, which allowed you to copy files from one computer to another over a
special parallel port cable, you can consider that connection a network as well. It
wasn’t very scalable (only two computers), or very fast, but it was a means of sending
data from one computer to another via a connection.
Connection is an important concept. It’s what distinguishes a sneaker net, in which
information is physically transferred from one computer to another via removable
media, from a real network. When you slap a floppy disk into a computer, there is
no indication that the files came from another computer—there is no connection. A
connection involves some sort of addressing, or identification of the nodes on the
network (even if it’s just master/slave or primary/secondary).
The machines on a network are often connected physically via cables. However,
wireless networks, which are devoid of physical connections, are connected through
the use of radios. Each node on a wireless network has an address. Frames received
on the wireless network have a specific source and destination, as with any network.
Networks are often distinguished by their reach. LANs, WANs, MANs, and CANs
are all examples of network types defined by their areas of coverage. LANs are, as
their name implies, local to something—usually a single building or floor. WANs
4
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Chapter 1: What Is a Network?
cover broader areas, and are usually used to connect LANs. WANs can span the
globe, and there’s nothing that says they couldn’t go farther. MANs are common in
areas where technology like Metropolitan Area Ethernet is possible; they typically
connect LANs within a given geographical region such as a city or town. A CAN is
similar to a MAN, but is limited to a campus (a campus is usually defined as a group

of buildings under the control of one entity, such as a college or a single company).
An argument could be made that the terms MAN and CAN can be interchanged, and
in some cases, this is true. (Conversely, there are plenty of people out there who
would argue that a CAN exists only in certain specific circumstances, and that
calling a CAN by any other name is madness.) The difference is usually that in a
campus environment, there will probably be conduits to allow direct physical
connections between buildings, while running fiber between buildings in a city is
generally not possible. Usually, in a city, telecom providers are involved in delivering
some sort of technology that allows connectivity through their networks.
MANs and CANs may, in fact, be WANs. The differences are often semantic. If two
buildings are in a campus, but are connected via frame relay, are they part of a
WAN, or part of a CAN? What if the frame relay is supplied as part of the campus
infrastructure, and not through a telecom provider? Does that make a difference? If
the campus is in a metropolitan area, can it be called a MAN?
Usually, a network’s designers start calling it by a certain description that sticks for
the life of the network. If a team of consultants builds a WAN, and refers to it in the
documentation as a MAN, the company will probably call it a MAN for the duration
of its existence.
Add into all of this the idea that LANs may be connected with a CAN, and CANs
may be connected with a WAN, and you can see how confusing it can be, especially
to the uninitiated.
The point here is that a lot of terms are thrown around in this industry, and not
everyone uses them properly. Additionally, as in this case, the definitions may be
nebulous; this, of course, leads to confusion.
You must be careful about the terminology you use. If the CIO calls the network a
WAN, but the engineers call the network a CAN, you must either educate whom-
ever is wrong, or opt to communicate with each party using their own language. This
issue is more common than you might think. In the case of MAN versus WAN
versus CAN, beware of absolutes. In other areas of networking, the terms are more
specific.