CCNA 2.0 Prep Kit 640-507 Routing and Switching

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CCNA2.0
Prep Kit
640-507
Routing and
Switching
1 Introduction to Cisco Certified Network Associate
Course 1
2 Overview of Industry Models and Standards 17
3 LAN Technologies 53
4 Internetworking 89
5 Router Basics 121
6 TCP/IP Addressing and the Protocol Suite 171
7 Routing Fundamentals 207
8 IPX/SPX Protocol Suite 245
9 Access Lists 273
10 Wide Area Networking (WAN) Technologies 311
11 Integrated Services Digital Network (ISDN) 351
12 Switching 375
13 Virtual LANs (VLANS) 411
14 Backup and Recovery 437
Appendixes
A Lab Exercises 461
B Using the CD-ROM and Test Engine 489
C ICMP Message Types/Troubleshooting 491
D Decimal to Hexadecimal to Binary Conversion 497
E Glossary 499
F Novell SAP Addresses 537
G TCP/UDP Port Numbers 539
H Commonly Used
show
Commands 541
I Objectives Index 543
Index 547
Heather Osterloh
A Division of Macmillan USA
201 West 103rd Street
Indianapolis, Indiana 46290
Contents
at a Glance
00 2887 FM 7/24/00 3:54 PM Page i
CCNA 2.0 Prep Kit 640-507 Routing and Switching
Copyright © 2000 by Que® Corporation
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International Standard Book Number: 0-7897-2288-7
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00 2887 FM 7/24/00 3:54 PM Page ii
Composed in AGaramond and Futura by Que Corporation.
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00 2887 FM 7/24/00 3:54 PM Page iii
Acknowledgements
For a project of this magnitude, there are many people to thank. I would like to
thank the following people:
All the staff at Macmillan Publishing, especially Rick Kughen, Tracy Williams,
and Matthew Luallen for all their support and advice.
Macmillan Publishing for believing in me and providing me with the opportu-
nity to write this book.
Larry Ginsburg, CCNP, CCNA, MCSE, who is a technical instructor and has
six years experience in the industry, for his help on many chapters in this book.
You can contact Larry at
sababa@onebox.com
.
My amazing team, Bill Barish and Jason Burita, who kept me focused—which
is an impossible task.
My parents, Rita and Karl, who always supported me in my quest for knowl-
edge and have always encouraged me throughout my life. They taught me the
best lesson of all, to see a goal and “make it so.”
To all the staff at IT Academy, Heather “Mini-Me” Whittington, Cindy,
Beverly, and Mike, who all had to make sacrifices for this book to be com-
pleted.
Laura Chappell, who first inspired me by introducing me to the world of net-
work certification.
To all my students, who continue to challenge me in class, and without whom I
would not have been inspired to write the best book possible.
And a special thanks to Dean Zerbe for his support.
My dogs, Cocoa and Kato, who stepped on my keyboard many times while I
was writing this book, forcing me to take a break and enjoy life for a second.
Most importantly, my husband Kirk, for putting up with all the hectic hours
and lack of sleep that went into completing this book. Without his support,
none of this would have been possible, and with his support, I believe that any-
thing is possible.
00 2887 FM 7/24/00 3:54 PM Page iv
About the Author
Heather Osterloh has earned industry recognition as a Cisco Certified Network
Associate (CCNA), Cisco Certified Design Associate (CCDA), Cisco Certified
Network Expert (CCNE), Cisco Certified Design Professional (CCDP), Network
Associate Sniffer trainer, Certified Network Expert, Novell CNI/ECNE, Microsoft
Certified Systems Engineer, and Microsoft Certified Trainer.
Having spent the last 14 years training and consulting worldwide, Heather is an
acknowledged leader in the networking industry. Currently, she has released the
ACRC and BCRAN Video Training Series for her CCNP Video Training Series.
Heather plans to finish the CCNP Series with a CLSC and CIT Video Series later
this year. In addition to Cisco-related videos, Heather has produced and authored a
multitude of training videos geared toward the busy professional.
Besides her popular video training series, Heather is founder and president of IT
Academy—an onsite training facility that specializes in Microsoft MCSE NT 4.0,
Windows 2000, CCNA, and CCNP Certification Training.
Heather has lectured and taught worldwide. She has lectured at the University of
California, Berkeley and at NetuCon’s NetWare User Conference in San Jose. She
also has taught and lectured at the University of Puerto Rico.
Heather currently lives in Northern California with her husband Kirk and her dogs,
Cocoa and Kato.
You can visit IT Academy’s Web page at
www.itacademy.com
. Or, you can contact
Heather via email at
book@itacademy.com
.
00 2887 FM 7/24/00 3:54 PM Page v
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00 2887 FM 7/24/00 3:54 PM Page vi
Table of Contents
1 Introduction to Cisco Certified Network Associate Course 1
Cisco Career Certifications 2
Network Support 3
Design 4
Routing and Switching, Network Support Certifications 4
CCNA 4
CCNP 5
CCIE 6
Routing and Switching, Design Certifications 7
CCDA 7
CCDP 8
Benefits of Certification 8
Electives 8
Security 9
Voice 9
Network Management 9
LAN ATM 9
SNA/IP Network Management 9
ISP Dial and WAN Switching 10
WAN Switching, Network Support 10
Testing 12
Test Composition and Layout 12
Test-Taking Strategies and Techniques 12
How to Use This Book 13
How This Book Addresses New Test Structures 13
What This Book Covers 14
How Each Chapter Is Organized 16
2 Overview of Industry Models and Standards 17
OSI Reference Model Background 18
The OSI Seven-Layer Architecture 20
Benefits of the OSI’s Layered Design 22
Layer Functions Clarified 23
Well-Defined Framework for Vendors 23
Reduced Networking Complexity 23
Simplified Troubleshooting 23
Specialization Promoted 24
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CCNA 2.0 Prep Kit 640-507 Routing and Switching
viii
General Description of OSI Layers 24
Application Layer 26
Presentation Layer 27
Session Layer 28
Transport Layer 30
Network Layer 33
Data Link Layer 35
Physical Layer 37
Connection-Oriented Versus Connectionless Protocols 38
Characteristics of Connection-Oriented Protocols 39
Connection-Oriented Protocols 39
Connectionless Protocols 40
Comparative Strengths of Protocols 40
Flow Control 41
Non-Sliding Window 41
Sliding Window 42
IEEE 802 Standards Overview 42
IEEE Data Link Sublayers 44
LLC Sublayer 44
MAC Sublayer 45
DoD 46
Chapter Summary 47
3 LAN Technologies 53
Before You Start 54
Ethernet and IEEE 802.3 54
The Evolution of Ethernet 54
Ethernet Versus IEEE 802.3 54
General Ethernet Operation 56
Slow Ethernet Specifications and Limitations 65
10Base5 (Thicknet) 65
Fast Ethernet Specifications and Limitations 69
Gigabit Ethernet 72
Gigabit Ethernet Overview 73
Token-Ring and IEEE 802.5 73
General Token-Ring Operation 74
FDDI and ANSI X3T9.5 78
General FDDI Operation 79
SAS Versus DAS 81
Chapter Summary 82
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ix
Contents
4 Internetworking 89
Network Addressing 90
Data Link (Layer 2) Addresses 90
Network Addresses 90
Internetworking Hardware 97
Physical Layer Segmentation Devices 97
Data Link Layer Segmentation Devices 98
Network Layer Segmentation Devices 108
Three-Layer Hierarchy 113
Chapter Summary 116
5 Router Basics 121
The Router 122
User Interface Components 122
Internal Router Components 123
Router Interfaces and Connectivity Components 126
Simulating WAN 130
Hyperterminal 132
Setup Dialog 134
AutoInstall 136
Command-Line Interface Configuration 137
Logging In 137
Navigating, Shortcuts, and How to Get Help 139
Command-Line Editing and Navigation Commands 144
Simple Configuration 146
configure terminal or config t Shortcut 148
configure network or config net Shortcut 148
configure memory or config mem Shortcut 148
Naming Your Router 148
Banner Messages and Interface Descriptions 148
Passwords and Optional Console Commands 150
Optional Console Commands 152
Configuring the Interfaces 152
Show Commands 155
Debugging 160
Cisco Discovery Protocol (CDP) 160
Remote Telnet Management 162
Chapter Summary 165
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CCNA 2.0 Prep Kit 640-507 Routing and Switching
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6 TCP/IP Addressing and the Protocol Suite 171
Understanding Binary to Decimal Conversion and Vice Versa 172
IP Addressing 174
Address Classes 174
Subnet Masks 177
Subnetting and Examples 182
Mapping the TCP/IP Protocol Suite to the DoD Model 187
Internet Protocols 187
Host-to-Host Protocols 195
Process/Application Layer Protocols 198
Troubleshooting Tools 200
Chapter Summary 202
7 Routing Fundamentals 207
Nonroutable Versus Routable Protocols 208
Basic Routing Concepts 208
Static Versus Dynamic 210
Routing Metrics and Costs 212
Administrative Distance 216
Static Routing 217
Configuring Static Routing 218
Distance Vector Routing (RIP, IGRP, and RTMP) 223
RIP 224
IGRP 230
Hybrid EIGRP 237
Link State Routing 238
OSPF 239
Chapter Summary 240
8 IPX/SPX Protocol Suite 245
Evolution of IPX/SPX 246
Mapping IPX/SPX to the OSI Model 246
Data Link Layer 247
Network Layer 250
IPX Routing Protocols 254
Transport Layer 257
Upper Layers 257
Configuring IPX Interfaces 262
Optional Steps 262
Configuring IPX RIP 265
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Contents
IPX Troubleshooting Commands 266
Chapter Summary 268
9 Access Lists 273
What Are Access Lists?274
Building Access Lists 275
Access List Types 276
Editing Access Lists 277
Removing Access List Lines 277
Wildcard Masks 278
Keywords 280
IP Standard Access Lists 280
Configuring IP Standard Access Lists 281
IP Extended Access Lists 287
IP Extended Access List Criteria 287
Configuring IP Extended Access Lists 288
Optional Parameters 289
Controlling Access to VTY Ports 294
Configuring VTY Filters 294
Named Access Lists 296
IPX Access Lists 297
IPX Standard Access Lists 297
Configuring IPX Standard Access Lists 297
IPX Extended Access Lists 299
Configuring IPX Extended Access Lists 300
Filtering IPX SAP Traffic 301
Configuring IPX SAP Filters 302
Chapter Summary 305
10 Wide Area Networking (WAN) Technologies 311
WAN Overview 312
WAN Connection Types 312
WAN Terminology 315
Serial Point-to-Point Connections 317
WAN Encapsulation Protocols 317
HDLC Encapsulation Protocol 320
Transfer Modes Supported by HDLC 324
Point-To-Point (PPP) 324
LCP Configuration Features 325
Configuring PPP Authentication and Multilink 327
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CCNA 2.0 Prep Kit 640-507 Routing and Switching
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Frame Relay 328
Frame Relay Terminology 329
Frame Relay Operation 330
Congestion Control 333
LMI 333
DLCI 335
Frame Relay Switch Mapping 336
Frame Relay Encapsulations 339
Preparing For Frame Relay Configuration 339
Frame Relay Configuration 342
Chapter Summary 346
11 Integrated Services Digital Network (ISDN) 351
Introduction to ISDN 352
Benefits of ISDN 353
ISDN Standards 353
ISDN Components 354
Basic Rate Interface 355
Primary Rate Interface 355
BRI Operation 356
ISDN Configuration Reference Points 357
Cisco ISDN BRI Interfaces 359
ISDN Switch Types 360
SPIDs 360
Configuring ISDN BRI 361
Dial On Demand Routing 363
DDR Basic Operation 364
Optional DDR Commands 367
Show and Debug Commands to Verify DDR Operation 368
Chapter Summary 370
12 Switching 375
Catalyst Switches 376
Catalyst Switch Functions 377
Switch Operation 378
Spanning Tree Protocol 386
Spanning Tree Operations 386
Initial Startup of the Catalyst Switch 390
LED Indicators 391
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Contents
Help Facilities and Basic Switch Commands 397
show running-configuration 399
show interfaces 399
Initial Configuration of a Switch 400
Configuring Switch Identification 402
Configuring the Switch IP Address 402
Port Security 406
Chapter Summary 407
13 Virtual LANs (VLANs) 411
VLAN Overview 412
VLAN Operation 413
Inter-Switch Link (ISL) Trunking 416
ISL Encapsulation 418
VLAN Trunk Protocol (VTP) 420
VTP Modes 422
VTP Pruning 423
VLAN Configuration 424
VTP Configuration 425
Configuring Inter-VLANs 431
Chapter Summary 432
14 Backup and Recovery 437
Reasons for Backup and Recovery 438
Configuration Register 438
Binary to Hexadecimal and Hexadecimal to Binary Conversion 439
Interpreting Register Settings 443
Alternative IOS Image Boot Methods 447
Setting Up TFTP from an Alternative Source 449
Password Recovery 453
Chapter Summary 456
A Lab Exercises 461
Equipment Requirements 462
Lab 1: Getting Started with Cisco Routers 462
Connecting Your Router 462
Installing HyperTerminal Software 462
Lab 2: Logging In and Getting Help 463
Logging In 464
How to Get Help 464
Terminal History 465
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Lab 3: Basic Router Configuration 466
Basic Router Configuration 466
Naming Your Router 467
Inserting Banner Messages and Interface Descriptions 467
Passwords 467
Lab 4: Configuring Interfaces 469
Configuring the Interfaces 470
Configuring Addresses 471
Providing Clocking 471
Lab 5: Examining Show Commands 472
Show Commands 473
Lab 6: IP Addressing 473
Decimal to Binary Conversion 473
Subnetting 474
Lab 7: Static Routes and Default Routes 474
Static Routes 474
Configuring RIP 475
Configuring IGRP 475
Show CDP 476
Lab 8: IPX/SPX Protocol Suite 476
Configuring IPX Interfaces 476
Configuring IPX RIP 477
Lab 9: Access Lists 477
Building Access Lists 477
Applying Access Lists 477
Lab 10: WAN Technologies 478
Configuring Frame Relay 478
Using Show Commands in Frame Relay 479
Lab 11: ISDN 479
Configuring ISDN BRI 479
Implementing DDR 480
Lab 12: Switching 481
Initial Startup of the Catalyst Switch 481
Accessing the Switch 481
Configuring a Switch 482
Lab 13: VLANs 482
VLAN Configuration 482
VTP Configuration 483
Mapping Switch Ports to VLANs 483
Configuring Inter-VLANs 484
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Contents
Lab 14: Backup and Recovery 485
Binary to Hexadecimal Conversion 485
Setting Up TFTP from an Alternative Source 485
Password Recovery 486
B Using the CD-ROM and Test Engine 489
Using the Test Pro Software 489
Equipment Requirements 490
Running the Test Pro Software 490
C ICMP Message Types/Troubleshooting 491
D Decimal to Hexadecimal to Binary Conversion 497
E Glossary 499
F Novell SAP Addresses 537
F TCP/UDP Port Numbers 539
G Commonly Used show Commands 541
H Objectives Index 543
Index 547
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1
CHAPT E R
Introduction to Cisco
Certified Network
Associate Course
01 2887 ch01 7/24/00 4:04 PM Page 1
Chapter 1 • Introduction to Cisco Certified Network Associate Course
2
This book was written with more than one goal in mind. The first goal is to prepare you
to take and pass the existing CCNA 640-407 or new 640-507, which was released in
summer 2000. This study guide should serve as an excellent tool for stepping through all
the exam objectives, enabling you to understand those objectives and topics with this
book as your primary or only written source. The other goal is to provide an excellent ref-
erence tool that will serve as a valuable addition to an information systems professional’s
technical library.
Cisco Career Certifications
On April 14, 1998 Cisco Systems, Inc. introduced the following certification tracks and
certification titles. Before then, the only certification that Cisco offered was the often-
touted, most-difficult, and most-prestigious title in internetworking, the Cisco Certified
Internetwork Expert (CCIE). Not only was this an all-or-nothing situation for industry
professionals to achieve, but the amazing difficulty of the CCIE exam and practical lab
test served as a deterrent to many.
With the explosion of job opportunities and growth in the internetworking field, the
advent of the new certification titles emerged to meet these increased demands (see
Figure 1.1). Today you have three separate certification tracks available with the possibil-
ity to earn certifications at each level of expertise:

Routing and Switching

WAN Switching

ISP dial
Currently, the most popular certification category is the Routing and Switching area. If
you choose the Routing and Switching track, you can earn certifications while you
progress and develop expertise by starting with the CCNA and moving to the CCNP and
the CCIE on the network support side. Or, if you prefer to focus on network design, you
can begin with the CCDA and move to the CCDP.
To keep track of new developments in training and testing, you can consult Cisco’s train-
ing Web site at
http://www.cisco.com/training/
.
The Routing and Switching certification has two certification disciplines—Network
Support and Design.
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CH
3
Cisco Career Certifications
Figure 1.1
Whether you choose the Network Support or Network Design side, Cisco offers differ-
ent levels of expertise and certifications for each track.
Network Support
Within the Network Support side, three certification levels are currently available:

CCNA (Cisco Certified Network Associate)

CCNP (Cisco Certified Network Professional)

CCIE (Cisco Certified Internetwork Expert)
CCIE Sylvan entry exam
Successful Cisco CCIE
2-Day lab exam
CCNA
Sylvan Prometric Exam
#640-407
NETWORK SUPPORT NETWORK DESIGN
CCNA
CCDP
CCIE
DCN
Sylvan Prometric Exam
#640-441
CCDA Certification
(Prerequisite)
CCNA Certification
(Prerequisite)
CCNP
Congratulations, you are a CCNA!
CCNA Certification
(Prerequisite)
Congratulations,
you are a CCDA!
Congratulations,
you are a CCDP!
65% + Achievement on the
CCIE Sylvan Entry Exam
(Prerequisite)
Congratulations,
you are a CCNP!
CCNA Certification
(Prerequisite)
BSCN #640-503
BCMSN #640-504
BCRAN #640-505
CIT #640-506
or
Foundation #640-509
Support #640-506
BSCN #640-503
BCMSN #640-504
BCRAN #640-505
CID #640-025
OR
Foundation #640-509
CID #640-025
CCIE
Successful Cisco CCIE 2-Day lab exam
Congratulations, you are CCIE!
Congratulations, you are a CCIE!
CCDA
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Chapter 1 • Introduction to Cisco Certified Network Associate Course
4
Design
Within the Network Design side, two certification levels are currently available:

CCDP (Cisco Certified Design Professional)

CCDA (Cisco Certified Design Associate)
Routing and Switching, Network Support
Certifications
This section summarizes the Cisco Routing and Switching support track certifications
from CCNA through CCNP and CCIE.
CCNA
The Cisco Certified Network Associate (CCNA) certification is the entry-level certifica-
tion within the Routing and Switching track. CCNA has two different exam tracks, the
old 1.0 Exam 640-407 and the new CCNA 2.0 640-507. Although Cisco has retired the
CCNA 1.0 training track for the 640-407, it still offers the exam based on that training.
Whatever exam track you select, the concepts you learn consist of an introduction to

The OSI model

Cisco IOS

IP addressing

Cisco router and switch hardware and configuration

Simple routed LAN/WAN configurations as well as switch LAN and VLAN con-
figuration
Each exam also covers

IP, IPX, and AppleTalk protocols

IP RIP, IPX RIP, and IGRP protocols
The exam covers some WAN solutions such as

Dial on demand routing (DDR) over ISDN

Frame Relay

Traffic filtering with access
Performance considerations with regard to accommodating different types of traffic are
also tested with network optimization questions.
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CH
5
Routing and Switching, Network Support Certifications
CCNA 1.0, Exam 640-407
CCNA Essentials is a Web-based learning tool covering basic router and switching con-
cepts, components, and configuration. CCNA Essentials combines the topics covered in
the two Cisco-certified instructor-led courses, ICRC (Introduction to Cisco Router
Configuration) and CRLS (Cisco Routers and LAN Switches) and the CD-ROM self-
paced training ITM (Internetworking Technology Multimedia).
CCNA 2.0, Exam 640-507
Exam 640-507 includes the same ITM CD-ROM–based training tool as the previous
track, but includes a choice of instructor-led Interconnecting Cisco Network Devices
(ICDN) or Web-based course ICDN-E, which is the same as the instructor-led ICDN
course, except it is offered over the Internet.
CCNP
The Cisco Certified Network Professional (CCNP) is the next level in Cisco certification
and expertise. The CCNP certification track is also in transition from the old exam track
CCNP 1.0 to CCNP 2.0. To qualify for The CCNP certification, the candidate must
already have his or her CCNA certification and pass

Routing Exam 640-403 (soon to be 640-503)

Switching Exam 640-404 (soon to be 640-504)

Remote Access Exam 640-405 (soon to be 640-505)
The candidate can also choose the foundation Exam 640-509, which covers the material in
the three previously mentioned exams. In short, one exam option breaks down subjects into
three individual exams, whereas Exam 640-509 covers all three subjects with one exam.
In addition to the single foundation exam or the combination of the switching, routing,
and remote access exams, the candidate must also pass the support Exam 640-506, previ-
ously known in the CCNP 1.0 track as 640-440.
CCNP 1.0
You must have a CCNA no matter what version you want to obtain. The following
courses cover the content of these exams:

ACRC (Advanced Cisco Router Configuration)

CMTD (Cisco Monitoring and Troubleshooting Dialup)

CLSC (Cisco LAN Switch Configuration)

CIT (Cisco Internetworking and Troubleshooting)
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Chapter 1 • Introduction to Cisco Certified Network Associate Course
6
CCNP 2.0
You must have a CCNA no matter what version you want to obtain. The following
courses cover the content of these exams:

The BCSN (Building Scalable Cisco Networks) course addresses information in
the routing exam.

The BCMSN (Building Cisco Multilayer Switched Networks) course covers infor-
mation in the switching exam.

The BCRAN (Building Cisco Remote Access Networks) course covers information
in the remote access exam.

The CIT (Cisco Internetwork Troubleshooting) course covers the information in
the support exam.
All these courses cover the essential concepts and skills needed to understand complex
routed LANs and WANs in addition to switched LANs and dial-up access solutions. A
great deal of this complexity derives from the protocols and concepts that appear in the
following sections.
Protocols

Major protocol suites, TCP/IP

IPX/SPX and AppleTalk

Routing protocols: IP RIP, IPX, RIP, IGRP, EIGRP, OSPF, and BGP
Concepts

VLSM and Route summarization

ISDN configuration

DSL technologies

DDR (Dial on Demand) routing over asynchronous and ISDN connections

Traffic queuing

ATM LANE configuration

Transparent and source route bridging
CCIE
The information covered in both the CCIE-R/S qualification exams is cumulative and
consists of all the information contained in both the courses required for the CCNP. The
CCIE is the most prestigious and by far the most difficult Cisco certification. Although
candidates for the CCIE must only have the CCNA as a prerequisite for taking the writ-
ten qualification exam, only a few thousand people have achieved the title of CCIE.
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CH
7
Routing and Switching, Design Certifications
The exam consists of two parts, a written qualification exam and a two-day lab. To qual-
ify for the lab, a candidate must first pass the written portion of the exam called the
CCIE-R/S qualification Exam 350-001. Until you pass the written portion, you cannot
participate in the lab portion of the exam.
The lab exam takes place over two days. The first day, a candidate has the task of setting
up a complex internetwork using disparate technologies. During the evening of the first
day, test administrators essentially sabotage the work you did that morning, so the second
day you spend troubleshooting and diagnosing those issues.
The CCIE exam has a high failure rate: Generally, more than 80% of first-time candidates
fail. Most candidates take the exam at least twice. In addition, if an exam administrator
feels that a candidate has not prepared, the administrator can fail the candidate at any
time. However, those who do make it through can reap the many rewards of having their
CCIE, which is motivation enough for many to accept the challenge. When you obtain
your CCIE, which is regarded as the pinnacle certification of the internetworking field,
you will literally have employers knocking at your door offering you job opportunities.
Routing and Switching, Design Certifications
Cisco offers two Design certifications for the Routing and Switching and WAN Switching
tracks, the Cisco Certified Design Associate (CCDA) and the Cisco Certified Design
Professional (CCDP).
CCDA
Cisco offers two Design certifications, the Cisco Certified Design Associate (CCDA) and
the Cisco Certified Design Professional (CCDP). You can achieve the introductory design
certification, CCDA, by passing the Cisco Design Specialist Exam 640-441. This exam
covers the basic theories and concepts of network design and the familiarity of the Cisco
product line. Candidates who already have their CCNA credentials can potentially
achieve their CCDA credentials through self-study.
A candidate must acquire these skills to pass the exam:

An understanding of network sizing

An understanding of the design of simple routed LANs and WANs

An understanding of the concepts of switched LANs and LAN emulation
Without this level of knowledge, a candidate has the best chance at passing by attending
the Designing Cisco Networks course. This course focuses on individuals who need a fun-
damental understanding of network design and the Cisco product line for either market-
ing purposes or for those wanting to make a transition to design-related roles.
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Chapter 1 • Introduction to Cisco Certified Network Associate Course
8
CCDP
The CCDP certification focuses on individuals with CCNP-level knowledge who would
like to translate those skills into the architectural and planning side of networking. To
achieve the CCDP certification, the candidate must first pass the CCNA and CCDA
exams. In addition, the candidate must pass the FRS Foundation Routing and Switching
Exam 640-509, in addition to the Cisco Internetwork Design Exam 640-025.
Or the candidate must pass the combination of Routing Exam 640-503, the Switching
Exam 640-504, the Remote Access Exam 640-505, and the Cisco Internetwork Design
Exam 640-025. Typically, someone who has already attained her CCNP certification and
wants to move toward a high-level network architecture position will add to her certifica-
tions by passing one additional test, the CID Exam 640-025.
Benefits of Certification
As a candidate progresses through the various Cisco certification levels, he has shown that
he has expanded his knowledge of networking with each level. More specifically, however,
he has added to his skill set and shown a certain level of proficiency in the subject matter
in addition to earning a powerful credential.
Many more significantly tangible benefits, such as recognition from an employer, can
translate into increased job responsibilities and opportunities. In addition, many employ-
ers will pay for employees to attend the training required for Cisco certification or reim-
burse the employee after she earns her certification.
Although compensation is based on many factors, a Cisco certification is among the
hottest certifications available in networking today, and with it comes a plethora of
opportunities for individuals with Wide Area Networking (WAN) skills, specifically those
using Cisco internetworking hardware.
For those with LAN administration or LAN engineering experience, obtaining a CCNA
certification demonstrates your capability in this area. It goes without saying that having
experience is no substitute for passing an exam, but either way, adding these skills will
only serve to increase your opportunities and can open doors.
Electives
Cisco offers specializations on the support side (CCNP) and design side (CCDP) that
allow you to emphasize core concentrations. Those who have already earned their CCNP
certification have several specializations available to them, including those discussed in the
following sections.
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9
Electives
Security
Managing Cisco Network Security (MCNS), Exam 640-442—This exam includes identi-
fication of security issues, configuration of PIX firewall product, and Cisco security fea-
tures for the purpose of locking down the network and securing it from outside access
from the Internet or remote dial-up sessions.
Voice
Cisco Voice Essentials (CVE) and Cisco Voice Over Frame Relay, ATM, and IP
(CVOICE) are covered in Exam 640-447. Topics include understand digital and analog
signaling and components. Configure Cisco 2600, 3600, 3810, and AS5300s for voice
over Frame Relay, ATM, and IP.
Network Management
Network management comes in two tracks:
1.
Track one:
Exam 640-444, Managing Cisco Internetworks (MCSI).
Exam 640-443, Managing Cisco Routed Internetworks (MCRI). Topics include
VLAN technologies and configuration, management tools used for switches,
RMON, and ATM.
2.
Track two:
Exam 640-501, Network Management, covers training through the instructor-led
course Cisco Enterprise Management Solutions (CEMS).
LAN ATM
Campus ATM Solutions (CATM), Exam 640-446—This exam covers ATM/LAN funda-
mentals and configuration, ATM LAN Emulation, IP Multicasting, SVC, and PVC con-
figurations.
SNA/IP Network Management
The SNA/IP Network Management elective consists of two exams, 640-445 (SNAM) and
640-456 (SNA/IP). The exams span six different courses that cover the following topics:
SNA concepts, terminology, routing, bridging and switching, SDLC, Serial tunneling,
Frame-Relay, APPN, and NetBIOS. The recommended training for the exams are

Cisco Data Link Switching Plus (DLSWP)

Frame Relay Access Support/Access Device (FRAS/FRAD)
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Chapter 1 • Introduction to Cisco Certified Network Associate Course
10

Advanced Peer-to-Peer Networking (APPN)

Channel Interface Processor (CIP)

SNA Configuration for Multiprotocol Administrators (SNAM)
Those with CCDP certifications can achieve specialization in SNA/IP integration, which
is Exam 640-457. The SNA to IP Migration training covers multiple protocol environ-
ments and how to migrate or allow for coexistence with SNA. Protocols covered are SNA,
APPN, IP and NetBIOS, Frame Relay, DLSW, mainframe support, and SNA to IP
Migration case studies.
ISP Dial and WAN Switching
Two additional certification tracks are available, although they have not achieved the pop-
ularity of the Routing and Switching track because they are even more specialized. Within
the WAN switching track, as with the Routing and Switching track, Cisco offers the
Network Support track with the CCNA, CCNP, and CCIE certifications; in the Network
Design track it offers CCNA, CCNP, and CCDP in WAN switching. Within the ISP
Dial track, Cisco offers just the CCIE certification.
The WAN switching certification track essentially focuses on the implementation of
Frame Relay and ATM networks. The Network Support certification begins with the
CCNA WAN-Sw 640-410, moving through the CCNPWS and culminating with the
CCIE; the certifications focus specifically on installation and troubleshooting of WAN
switches using Cisco Strata View, IPX, IGX, BPX, AXIS, and modems.
The Design-track candidates must achieve both CCNA- and CCNP-level certification
within the Support track in addition to the CCDP requirements for this track.
WAN Switching, Network Support
If you want to achieve a certification on the Network Support side of WAN Switching,
you must have or pass the following:

CCNA WAN-Sw, Exam 640-410—Covers the terms, concepts, and configuration
of WAN switches and concentrators.

WQS, WAN Quick Start—CD-ROM training tool.

ICWS, Installation of Cisco WAN Switches—Instructor-led CCNP WAN-Sw. To
achieve this certification, you must be familiar with Cisco’s IGX, BPX, and MGX
switch and concentrator hardware for WANs, and its hardware, administration,
and configuration for ATM and Frame Relay networks.

Candidate must already possess the CCNA WAN-Sw certification.
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11
ISP Dial and WAN Switching

MSSC, Multiband Switch and Service Configuration, Exam 640-419.

MACC, MGX ATM Concentrator Configuration, Exam 640-411.

SVIO, Cisco StratView Plus Installation and Operations (SVIO), Exam 640-451
or Exam 640-422.

CCIE status is achieved by passing the WAN switching CCIE exam and the two-
day lab.
Design WAN Switching
To achieve this certification you need the following minimum requirements:

CCNA WAN-Sw

CCNP WAN-Sw

DSWVS, Designing Switched WAN and Voice Solutions, Exam 413
This curriculum should provide an individual with a clear understanding of how to
design and implement complex WAN-switched networks, support ATM and Frame
Relay, use modeling tools, implement X.25 and ISDN, and identify and troubleshoot a
complex WAN.
CCIE ISP Dial
The CCIE ISP Dial certification focuses on the WAN engineering needs of ISPs. For
example, some of the points addressed in the exam focus on the following protocols and
skills:

ISDN

T1 and E1 signaling

ATM

Frame Relay

SMDS

xDSL

X.25

IP tunneling

VPDN

QoS

Authentication and Encryption servers

CIDR
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Chapter 1 • Introduction to Cisco Certified Network Associate Course
12
Testing
At this time, only the Sylvan Prometric testing centers administer Cisco testing. Sylvan
Prometric testing centers can be reached at (800) 755-3926 or (800) 204-EXAM. They
operate Monday through Friday between 7:00 a.m. and 6:00 p.m. Central time. You may
also schedule your exam online at Cisco’s Web site, at
www.cisco.com/warp/public/10/wwtraining/certprog/testing/register.htm
.
You must schedule your exam 24 hours before exam time. In the event of cancellation,
you must cancel within 24 hours of an exam.
In addition, unlike with Microsoft or Novell testing, you may take only one Cisco exam
per day. As with similar computer-based certification exams, testing centers do not allow
any personal items or materials in the testing room. They provide you with a pencil and
paper or a dry-erase sheet and pen.
Test Composition and Layout
The CCNA exam consists of 80 multiple-choice questions, for which the candidate has
90 minutes allotted to complete the test. To pass, a candidate must score 755 points out
of a possible score of 1000. The exam costs $100 and can be taken only through Sylvan
Prometric.
Recently, Cisco changed the operation of the exam. Unlike with Microsoft tests, ques-
tions cannot be marked or skipped and returned to later. The candidate must answer each
question consecutively for the exam to continue, and that answer choice is final.
Although the exam consists of multiple-choice questions, many questions have more than
one correct answer. Many questions have up to five or six answer choices, and this makes
using the power of elimination more difficult. Test makers draw the questions from nine
different topics, and the percentage from each topic varies from exam to exam.
Test-Taking Strategies and Techniques
After you enter the testing room, you do not have to immediately begin your exam.
When the test begins, we recommend that you first write down any pertinent informa-
tion, such as command syntax, and any pertinent tables or specifications. Taking this time
to write down pertinent information gives you not only a time to perform recall and writ-
ing but a chance to relax. During this time, take a few deep breaths and take your test
confidently. Remember, an important factor in all test taking is frame of mind.
When preparing for the exam, use the companion CD-ROM located in the back of this
book. The CD-ROM includes a test engine with hundreds of practice test questions.
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How to Use This Book
When taking the sample tests, eliminate the answers that are absolutely incorrect. This
will lead you to a short list of answers that are possibly correct.
When taking the real exam, keep track of your time. Time goes by very quickly, so try
not to spend too much time on one question. Spending too much time on a question
that you are unsure of can make you race through questions that you know the answer to,
causing you to answer them incorrectly.
How to Use This Book
The information contained in this book covers all the concepts, terminology, and exer-
cises necessary to pass either the CCNA Exam 640-407 or 640-507. This includes every-
thing from identifying the physical components of the router and turning it on for the
first time to configuring multiple protocols and access lists for traffic filtering. Unlike
many books available on the CCNA subject matter today, this book uses many visual aids
in the form of screen shots, which help you understand and visualize the process that the
router is performing with the various user-issued commands in the exercises. This visual-
ization should benefit you and help in the learning process.
To comprehend the material in this book, you must walk through the lab exercises
included in Appendix A, “Lab Exercises.” This means using a physical router (we recom-
mend a Cisco 2503 because it has all the necessary hardware components) and a Cisco
Catalyst 1900 switch or router and switch-simulation software.
There is really no substitute for hands-on exercises, and performing the exercises in the
book should make the exam process much more comfortable. Performing the exercises
will make you more comfortable when taking the exam because the CCNA exam expects
you to be able to explain switching and routing theory in a real job situation and to per-
form those tasks by recognizing the function of the command sets explained in this book.
How This Book Addresses New Test Structures
This book addresses all the topics necessary to prepare you for the CCNA certification
Exam 640-507. Again, we stress that you should participate in the lab exercises, either
with a router or with router simulation software.
Exam number 640-507 replaces Exam number 640-407, and, of course, has differences.
The new test puts additional emphasis on Cisco’s 1900 series switch, focusing on basic
switching skills and understanding more switching theory and methods, including VLAN
configuration. In addition, it also places more emphasis on ISDN configuration and
back-up scenarios. This book takes an updated approach to other books and covers ISDN
and switching theory and methods in more depth than other books.
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Chapter 1 • Introduction to Cisco Certified Network Associate Course
14
What This Book Covers

Chapter 1, “Introduction to Cisco Certified Network Associate Course,” provides
an overview of the different certifications you can obtain, test layout, and strategies
and how to use this book.

Chapter 2, “Overview of Industry Models and Standards,” gives an in-depth
description of the seven-layer architecture of the OSI Reference Model. This OSI
model provides a framework that will be used throughout the book. This chapter
also covers connection-oriented and connectionless protocols.

Chapter 3, “LAN Technologies,” introduces LAN technologies. This chapter cov-
ers Ethernet and IEEE 802.3 and Token-Ring and IEEE 802.5.

Chapter 4, “Internetworking,” introduces network addressing and network hard-
ware. This chapter also introduces switching methods and VLANs.

Chapter 5, “Router Basics,” gives you your first hands-on experience with
routers. This chapter covers all the router’s parts and how it works. In addition, it
walks you through the various configurations, aiding you with a variety of screen
shots.

Chapter 6, “TCP/IP Addressing and the Protocol Suite,” introduces Network layer
addressing, including TCP and IP. This chapter discusses the five different address
class types and maps TCP/IP to the DoD model.

Chapter 7, “Routing Fundamentals,” looks at basic routing concepts, including
static versus dynamic routing and what a router needs to know to function. This
chapter also takes an in-depth look at Distance Vector routing.

Chapter 8, “IPX/SPX Protocol Suite,” maps IPX and SPX protocols to the OSI
Model. This chapter walks you through the Data Link layer to the upper layers
as it examines each layer’s function in regards to the two different protocol
suites.

Chapter 9, “Access Lists,” explains how to use access lists to filter traffic. This
chapter focuses on the two different kinds of access lists: standard and extended.

Chapter 10, “Wide Area Networking (WAN) Technologies,” introduces you to the
world of WAN technologies. This chapter thoroughly explains Point-to-Point and
Frame Relay.

Chapter 11, “Integrated Services Digital Network (ISDN),” introduces you to
ISDN. This chapter focuses on ISDN components and the benefits of ISDN. This
chapter also takes an in-depth look at Dial on Demand Routing (DDR).
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How to Use This Book

Chapter 12, “Switching,” focuses on how Cisco 1900 switches work. This chapter
stresses filtering and buffering, forwarding mechanisms, network management,
and backplane bus architecture.

Chapter 13, “Virtual LANs (VLANS),” focuses on VLAN technologies. This
chapter stresses Inter-Switch Linking (ISL), ISL Encapsulation, and VLAN Trunk
Protocol (VTP). It also guides you through the steps of VLAN and Inter-VLAN
configuration.

Chapter 14, “Backup and Recovery,” discusses how to protect your network when
a router fails to load a primary image from Flash. The chapter discusses loading
your IOS from a TFTP server, configuration register, and other precautionary
measures. Compared to other CCNA books, this book has the only real “Backup
and Recovery” section available.

Appendix A, “Lab Exercises,” walks you through various hands-on exercises. In
this appendix, you perform various router and switch configurations. In addition,
this appendix has you display
show
command functions and perform binary-to-
hexadecimal conversions and backup and recovery techniques.

Appendix B, “Using the CD-ROM and Test Engine,” is a guide that helps you
understand and use the CD-ROM and test engine that accompanies this book.

Appendix C, “ICMP Message Types/Troubleshooting,” gives you a list of ICMP
message types, which you will find useful when troubleshooting.

Appendix D, “Decimal to Hexadecimal to Binary Conversion,” provides a table
that has conversions for decimal, hex, and binary.

Appendix E, “Glossary,” provides definitions of terms used in this book.

Appendix F, “Novell SAP Addresses,” lists Novell SAP addresses that are used to
identify the upper-layer process that is being advertised.

Appendix G, “TCP/UDP Port Numbers,” lists common TCP/UDP port numbers,
which helps identify well-known ports for protocols, and a description of each
port.

Appendix H, “Commonly Used
show
Commands,” gives you a list of commonly
used
show
commands. You will find this to be a useful list of commands.

Appendix I, “Objectives Index,” is a mapping document and is updated to reflect
the new test objectives for Exam 640-507. Use this appendix to look up exam
objectives and the section in which they are covered in the book. This should
prove to be a helpful study guide.
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Chapter 1 • Introduction to Cisco Certified Network Associate Course
16
How Each Chapter Is Organized
Each chapter includes the following items to help guide your studies:

Chapter Prerequisites—Each chapter opens with a list of prior reading that will
help you get ready for a particular topic. Generally, if you read the chapters in
sequential order, you will be ready for each topic as it arises.

“While You Read” Chapter Pretest—These questions guide you as you read the
chapter. They’ll also help you determine whether you already know the material
covered in the chapter, saving you valuable study time.

Key Concepts—Key Concepts boil down a topic to help you prepare for a test.
These elements also point out tricky or commonly asked test questions. Read
these!

“While You Read” Chapter Pretest Answers—You’ll find answers to the While You
Read questions at the end of the chapter in which the question appears.

Chapter Practice Test—Each chapter includes a set of 10 questions that mimic
what you’re likely to see on the actual exam. You should be able to answer the
practice test questions in each chapter before taking the CCNA exam.

Flash Notes—The removable booklet just inside the front cover of this book is
your portable guide to the bare essentials you’ll need to know for the test. Use this
for last-minute cram sessions.
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2
CHAPT E R
Overview of Industry
Models and
Standards
WHI LE YOU READ
1.What do the terms LAN and WAN stand for?
2.Why do we have the OSI model?
3.What are the various layers that comprise the OSI model?
4.What are the functions of each layer within the OSI model?
5.What are the various IEEE standards?
CHAPTER PREREQUISITE
Before beginning this chapter, you
should be familiar with general
networking and protocols con-
cepts, preferably TCP/IP. You also
should be familiar with operating
systems, such as Windows 95 and
Windows NT.
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Chapter 2 • Overview of Industry Models and Standards
18
OSI Reference Model Background
In the early days of networking, all systems and protocols were proprietary. Operating sys-
tems developed by large companies, such as IBM’s SNA and Digital Equipment
Corporation’s DECNet, included proprietary protocol suites. These operating systems and
their corresponding protocols were created primarily to facilitate mini- and mainframe
network communication, and no provisions had been made for interconnection or to
enable for communication with outside systems. When SNA and DECNet were devel-
oped, no one had anticipated the prevalence of mixed computing environments that
exists today, and only systems using compatible protocols and operating systems could
communicate with each other and exchange data.
Because intercommunication between these different proprietary systems was difficult at
best, if not altogether impossible, some type of protocol translation was called for to
address the problem faced by companies wanting to communicate and share information
with one another, but that were lacking a framework to do so. The Department of
Defense (DoD) developed an intercommunication model in the early 1970s; however,
this model became obsolete when the ISO completed development of the OSI Reference
Model in the early 1980s. The OSI Reference Model consists of a seven-layer architecture
that defines the different networking functions that occur at each layer (see Figure 2.1).
Application Provides services to user applications
Presentation
Data translation, conversion,
encryption, decryption, compression
Session Session management and dialog control
Transport
Reliable end-to-end connection between
programs/processes
Network Logical addressing and routing
Data Link Frame transmission and reception
Physical Signal encoding, media and connectors
OSI Model and Functions
Figure 2.1
The OSI Reference Model defines the seven layers and their functions.
Later in this chapter you will find a further discussion of the DoD model and its layer
mapping to the OSI model.
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OSI Reference Model Background
The purpose of the OSI Reference Model is to enable both similar and dissimilar systems
to communicate with each other seamlessly by providing an architectural framework for
vendors and manufacturers to follow when designing their hardware, protocols, and oper-
ating system environments, and to provide engineers and developers with standard speci-
fications for system intercommunication. With a standardized, layered approach,
communication between both similar and dissimilar networks is possible and enables the
use of different protocols in different network architectures and lower-layered media
types. Although seamless communication is not always achieved, it is the primary goal of
the OSI Reference Model.
The many protocols in existence prior to the OSI model did not lend themselves easily to
interconnectivity. In most cases, retrofitting these protocols was unfeasible. Therefore,
most protocols and hardware currently being implemented by vendors and manufacturers
conform to the guidelines of the OSI model. The smooth and swift exchange of data and
seamless interconnectivity required in today’s mixed computing environments depend on
manufacturers and vendors adhering to a standardized reference model. The OSI
Reference Model’s architecture provides manufacturers and vendors with the level of con-
sistency and flexibility necessary to achieve ease of interconnectivity in today’s computing
environment.
The OSI model is a conceptual framework. It consists of a series of standards defining
what is supposed to happen and how to package data for it to go out on the wire to a
remote host. How the functionality occurs at each layer is up to the vendor or manufac-
turer who creates or implements the hardware or protocols. Sometimes vendors adhere
very closely to the standards and sometimes they don’t. The end result is not always seam-
less compatibility between dissimilar devices; however, this framework and model is the
best resource available to enable this compatibility.
These logical layers of the model do not define specifically what must be performed at
each layer; instead, they simply define which functions reside at each respective layer.
Individual manufacturers are free to interpret and decide how closely they want to adhere
to the specifications for a given layer.
In an overall sense, each layer has distinct functions that must occur within it to prepare
data to go out on the wire to communicate with a remote station. The vendor can deter-
mine the specifics within the general functions; in other words, the manufacturer or
developer defines how those specifics work, so vendors must concern themselves with
only their parts of the puzzle. As long as an organization or vendor follows the guidelines
laid out by the ISO for a developer’s particular layer, the result is a product that is easy to
integrate with other products that also follow the model.
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Chapter 2 • Overview of Industry Models and Standards
20
It is important to keep in mind that the OSI is used only when you are packaging data
for transmission to connect to a remote host, similar or dissimilar (one using the same
protocols and same operating system you are, or not).
The OSI Reference Model is not used when accessing data locally on a system. For exam-
ple, to access file and print services, you would simply access as usual a local computer’s
hard drive and open a local application. In this situation, no user intervention is required
to access the data. However, if you want to perform that same function on a remote host,
you must somehow send a message to the other device to access files or a printer, and
have that device respond to you by transferring the data. To redirect the request of access-
ing a file or print services, you must have a redirector. Then, you must prepare that trans-
mission or packet with header and control information and send it over the wire to the
remote device so that it knows what to do with the data and how to respond.
According to Cisco, five steps to converting data for transmission over the wire exist:
1.
The upper three layers of the OSI (Application, Presentation, and Session layers)
convert user data into messages.
2.
The Transport layer converts messages into segments.
3.
The Network layer converts segments into packets or datagrams.
4.
The Data Link layer converts packets or datagrams into frames.
5.
The Physical layer converts frames into bits and encodes them on the wire as elec-
trical signals or light pulses, depending on the media type.
These five steps for converting data to be transmitted on the wire appear in Figure 2.2.
Key Concept
For the exam, you will need to know the conversion function and which layer it
applies to in the OSI model.
The OSI Seven-Layer Architecture
The OSI model has seven layers (from top to bottom):

Application

Presentation

Session

Transport

Network
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CH
21
The OSI Seven-Layer Architecture

Data Link

Physical
“Messages”
H
1
Application
“Messages”
H
2
Presentation
“Messages”
H
3
Session
Segments
H
4
Transport
Datagrams & Packets
H
5
Network
Frames
H
6
Data Link
Bits (1 0 1 0 1’s)
H
7
Physical
User Data
Data Encapsulation
Five Steps to
Converting
Data to be
Transmitted
on the Wire
Figure 2.2
User data encapsulation involves five steps.
To make familiarization and memorization of the order of the layers easier, it’s useful to
try a little word association. These examples go from the top layer to the bottom, and
vice versa (see Figure 2.3).
All
People
Seem
To
Need
Data
Processing
Away
Pizza
Sausage
Throw
Not
Do
Please
Application
Presentation
Session
Transport
Network
Data Link
Physical
Bottom Up
Top Down
Figure 2.3
It is helpful to use word associations to remember the different layers of the OSI
Reference Model.
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Chapter 2 • Overview of Industry Models and Standards
22
Key Concept
You must know not only the order of the layers for the exam, but also which func-
tions are performed at each layer. Refer to Figure 2.1 for the layers and func-
tions.
Key Concept
Systems implement the Physical and Data Link layers of the OSI model using
hardware and software; the Network layer involves routers; and the Transport,
Session, Presentation, and Application layers involve software only.
Benefits of the OSI’s Layered Design
The layered design of the OSI Reference Model provides benefits not only for manufac-
turers and software developers, but also for those individuals, such as network engineers,
who offer support and troubleshooting.
The OSI model’s benefits can be broken down as follows:

Makes general functions of each layer clear

Provides a well-defined framework for vendors to use in writing applications and
developing hardware

Reduces complexity of networking by compartmentalizing model functions

Promotes interoperability between dissimilar networks and protocols

Simplifies troubleshooting by reducing the focus for locating network complica-
tions

Accelerates evolution in the industry by facilitating specialization
Key Concept
You must be familiar with at least three reasons why the industry benefits from
using the OSI Reference Model.
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Benefits of the OSI’s Layered Design
Layer Functions Clarified
By narrowing the scope of a layer’s responsibility, the OSI model eases the developmental
and support burdens manufacturers and network engineers must address in their work.
Additionally, the minimized responsibility of each layer prevents individuals from having
to reinvent the boundaries of a product or protocol for a desired use.
Well-Defined Framework for Vendors
Vendors can write their specifications to one layer or multiple layers. A layered approach
removes much of the complexity and enables vendors to focus and specialize on only their
particular layer of the OSI model. This also improves interoperability between systems, as
well as provides an open environment in which multiple protocols can coexist. For exam-
ple, a vendor or manufacturer who creates a network interface card can simply work with
the Data Link layer of the OSI model, eliminating the necessity of working beyond the
scope of that particular device. Other vendors would have that responsibility instead.
The modular design of the OSI enables vendors to produce specialized products. They
don’t need to address all functions from top to bottom; instead, they can focus on a par-
ticular layer and function of the OSI model, so releasing hardware or software is easier.
A certain amount of variation exists among vendors in terms of how closely they adhere
to each layer’s conceptual guidelines. In spite of these differences, the very existence of a
standardized model increases both the current level of interoperability between systems
and the likelihood that future protocols and products will coexist harmoniously on the
same network.
Reduced Networking Complexity
The layered approach also enables network engineers to apply a divide-and-conquer
approach to troubleshooting. After you know what is supposed to happen at each layer,
you can identify when something is not working based on which layer is not performing
its function. That protocol or piece of hardware is supposed to function according to the
specifications defined at that layer. If it’s not functioning, it enables you to use that model
to isolate and compartmentalize the problem, making troubleshooting much easier.
Simplified Troubleshooting
Perhaps more importantly, the model provides seven smaller pieces with which to work,
instead of forcing users to focus on the whole structure to locate problems. Overall, this
causes network operations in general to function as simpler pieces rather than a single,
more complicated entity.
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Chapter 2 • Overview of Industry Models and Standards
24
Specialization Promoted
Finally, the use of a widely accepted, industrywide set of guidelines for networking will
inspire ever faster and more reliable programs and protocols. Knowing they can compete
at any layer of the OSI Reference Model to improve on the specifications and perfor-
mance, manufacturers and vendors are inspired to push efficiency to the utmost limits.
General Description of OSI Layers
When you are getting ready to send data (and when we say data, this could mean any-
thing from an email message to a request to read a file from a remote host), that request
must be packaged and redirected. The system must apply addressing to it, associate proto-
cols with it, modulate it, and send it out on the wire. This process is based on the specific
functions of the OSI Reference Model.
Each layer in the OSI model helps provide header and control information so that a peer
layer in the remote host can remove that header and control information and know what
to do with it. When a system is preparing data to be sent out on the wire, the first thing
that occurs is a redirector captures the message, places its header and control information
on it, and sends it down to the next layer. Lower layers in the OSI model provide upper-
layer support services. These can include reliable transport services, routing services, con-
nection-oriented services, connectionless services, and addressing services. All this helps
prepare the data to go out on the wire. The message could be as simple as “Hi” from one
user to another, but these services still apply.
Each layer has a distinct role to play in preparing data to be sent out on the wire to com-
municate with a peer remote host (see Figure 2.4). All the steps inherent to these roles are
transparent to the user.
For example, say I’m a vendor creating a network interface card—such cards have drivers,
as well as the circuitry, associated with them. I am responsible only for providing the soft-
ware to control my hardware and actually building the hardware itself. I do not have to
concern myself with what type of protocol runs on top of that hardware, nor with the
operating system.
When the computer passes data from one layer to the next, each layer must add header or
control information to the data. Each layer adds this information as the data makes its
way down to the Physical layer and the actual physical media, such as the wire or network
cable. This process is similar to an envelope being placed inside another envelope at each
layer.
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General Description of OSI Layers
Figure 2.4
Each layer of the OSI model adds header and control information used by the corre-
sponding layer at the receiving host.
For example, the Application layer provides header and control information to the peer
Application layer at the remote host location. This header and control information, along
with the data, is passed down to the next level, the Presentation layer. The Presentation
layer reads the upper layer’s information as data but disregards the header and control
information because it adds its own encryption. The Presentation layer’s header and con-
trol information is provided to the peer Presentation level at the remote host. Each layer
adds header and control information and sends the data down to the next level, and the
computer adds this information as the data passes through each layer.
After the data gets to the Data Link level, the system runs an algorithm called a Cyclical
Redundancy Check (CRC) or a Frame Check Sequence (FCS). The CRC is added as a
trailer to the end of the information to guarantee that the bits being sent are the same bits
the end host receives, and that they indeed match. The term frame refers to the logical
grouping of information that data undergoes at the Data Link layer. From there, the data
goes out on the wire as electrical or light signals—1s and 0s—and is received by the
intended remote host (see Figure 2.5).
Upon reception, this process is reversed. Each layer removes its header information and
passes the data up to the next layer, exposing that layer’s header and control information
and data, until it arrives at the Application layer. The Application layer then strips off its
own header and control information and passes the data up. All this must happen with
every single frame that goes out on the wire. Header and control information must be
attached so the communication can identify where it’s going and who sent it.
Data
AH
PH
SH
TH
NH
DH
DT
Bits
Data
AH
PH
SH
TH
NH
Data
AH
PH
SH
TH
Data
AH
PH
SH
Data
AH
PH
Data
AH
Data
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
Layers Operate as Peers
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Chapter 2 • Overview of Industry Models and Standards
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Figure 2.5
The receiving host removes headers and trailers before sending data up to the next
layer.
Application Layer
The top layer of the OSI model can be confusing because people think it refers to user
“applications” such as Word, Excel, PowerPoint, and so on. The Application layer is not
the software applications themselves, but rather a window that enables you to provide
data access from one application to another across a network, and a window to the OSI
Reference Model to prepare your data to be packaged and sent out on the wire.
The Application layer gives user applications the capability to send data across the net-
work. It simply affords access to the lower layers, or provides a window to the OSI model.
Unlike the other OSI layers, this layer does not provide services to any of those other lay-
ers but, instead, is restricted to providing access for the applications only.
For example, when you access your email program or start a Telnet client application, you
must specify the data you are going to send. In addition, that data must be prepared
before it is sent out on the wire. Application layer services also provide access to file and
print services. Examples of Application layer services you might be familiar with are
Microsoft’s SMB-based client redirector and the server responder, which are implemented
as filesystem drivers (
RDR.sys
and
SRV.sys
, respectively).
If you use Windows NT, your client redirector is considered an Application layer proto-
col. When you make a request for file and print services of a remote NT box, your redi-
rector piece must take that information and prepare it for the next layer. That adjacent
layer gets it ready to send over the wire. Then, when that information is sent to the
remote host, the receiving layer at the other end is the Application layer. This layer on the
remote host corresponds to the server service. Thus, the client requester piece and the
server responder piece in Windows NT are considered Application layer services that pro-
vide requests and responses on behalf of an application.
Application
Presentation
Session
Transport
Network
Data Link
Physical
Messages
Messages
Messages
Segments
Datagrams or Packets
Frames CRC
Bits 1 0 1 0 1 0 s
H
1
H
2
H
3
H
4
H
5
H
6
Headers and Trailers
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General Description of OSI Layers
Some of the Application layer services include providing the following:

Applications with network and inter-network services

File and print services

Email

Web access and HTTP

Telnet access on a remote host

File transfer protocol (FTP)
Remember, the Application layer’s job is to provide an interface to your protocol stack.
Presentation Layer
The next level is the Presentation layer. The function of the Presentation layer is to pro-
vide a common data format across different platforms.
The Presentation layer is responsible for the following:

Data conversion and translation

Compression/decompression

Encryption/decryption

Multimedia and sound
Key Concept
The Presentation layer formats information in such a way that it makes the oper-
ating system transparent. For the test, you must distinguish between different
Presentation layer protocols, such as text-related/data-related, image-related,
and multimedia-related.
Table 2.1 shows commonly used protocols in the Presentation Layer.
Table 2.1 Commonly Used Protocols
Text- and data-related protocols ASCII
EBCDIC
Encryption/decryption
…continues
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Chapter 2 • Overview of Industry Models and Standards
28
Graphics or image-related TIFF
Presentation layer protocols JPEG
PICT
GIF
Multimedia-related protocols MIDI
MPEG
QuickTime
You should be able to identify all these as Presentation layer protocols.
Another example of a true Presentation layer protocol is eXternal Data Representation
(XDR). Sun Microsystems uses this protocol in its client/server–based Network File
System (NFS) implementation. NFS uses XDR, which is actually incorporated into the
programming code, to provide platform independence.
Several protocols existed prior to the introduction of the OSI Reference Model and there-
fore don’t truly map to it. As a result, vendors often implement protocols that perform
functions covering the top three layers: Application (access to the stack), Presentation
(formatting of data), and Session (connection services). Therefore, protocols can cover
more than one layer and can skip layers.
Session Layer
The Session layer manages and sets up sessions. A session consists of a dialog between
Presentation layers on two or more systems. This layer also handles the requests for differ-
ent services between systems and manages the responses to those requests between sys-
tems. In addition, it controls the dialog between two applications on different hosts and
manages data streams.
The efficiency of dialog control between hosts in the Session layer depends on whether
the communication mode is half-duplex or full-duplex. In a half-duplex configuration,
only one device can communicate or transmit at a time, while all others are in standby
mode awaiting their turns. Each side must wait until the other process has finished send-
ing and then respond with a separate acknowledgement. Conversely, a full-duplex com-
munication can send and receive at the same time and is therefore much more efficient
than half-duplex communication. Full-duplexing accomplishes its efficiency by piggyback-
ing, or including data within the same frame.
Table 2.1 continued
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General Description of OSI Layers
The Session layer includes

NFS

SQL

X Window

NetBIOS

RPC
An example of a Session layer protocol you might be familiar with is the Network Basic
Input Output System (NetBIOS). NetBIOS sets up a session between two Windows NT
or Windows 95 machines. NetBIOS, which IBM and Sytec developed about 20 years
ago for use on flat-bridged networks, is a true Session layer protocol used by Microsoft
and provides name services and session management between two devices using simple
naming.
Originally, NetBIOS was used in combination with NetBIOS Extended User Interface
(NetBEUI), which, like NetBIOS, is a non-routable protocol. These protocols can be
confusing because they were implemented together into firmware. If you were using
NetBIOS, you were running it over NetBEUI; if you were using NetBEUI, you were
using it with NetBIOS. In other words, no distinction existed, so most people say that
neither one is routable, which is true. However, if you transport NetBIOS over a routable
protocol, such as IP or internetwork packet exchange (IPX), NetBIOS is routable. If you
install it on NT Workstation or Windows products, it gives you the option of installing
IP, IPX, and/or NetBEUI.
Sun Microsystems developed NFS to facilitate access to file and print services on UNIX
hosts.
Key Concept
As far as Cisco is concerned, NFS is a Session layer protocol. However, NFS is
truly an Application layer protocol.
RPC, also developed by Sun, enables clients to make requests for remote execution. These
requests are sent to a remote host for processing and a response. It also enables communi-
cation between two hosts across a network. In addition, NFS uses RPC to send calls and
get responses at the Session layer and uses XDR at the Presentation layer.
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30
Also at the Session level, IBM developed Structured Query Language (SQL), which is a
client/server–based language that provides a set of commands and the capability to
manipulate data stored in databases. The information is compiled in SQL, which is a
standard from various manufacturers. Additionally, the databases that use it are the
favored backend for Web site data management.
Key Concept
SQL is regarded as an Application layer protocol; but again, Cisco views it as
residing at the Session layer.
Another protocol, X-Window, provides the capability to put a graphical frontend on an
otherwise command-driven UNIX interface.
Transport Layer
The Transport layer is responsible for the proper sequencing of data and its error-free
delivery.
The Transport layer does the following:

Controls end-to-end communication between two processes running on different
hosts

Provides connection-oriented or connectionless services to upper layers

Uses client and server port addresses to identify processes running within a host

Segments data for upper-layer applications
The Transport layer is typically known for providing the following transport-oriented
services:

Reliable, guaranteed delivery

Error control

Flow control

Sequencing

Acknowledgement

Connection setup and teardown

Recovery

Retransmission
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General Description of OSI Layers
Note, however, that you also can have protocols at the Transport layer that do not provide
reliable services.
The Transport layer is responsible for identifying which processes are communicating on
each host and providing either connection-oriented services and reliable transport or
speed of delivery. It manages the data flow and deals with flow control in a connection-
oriented session.
The best-known protocols at the Transport layer are

Transmission Control Protocol (TCP)

User Datagram Protocol (UDP)
Others include

NetWare Core Protocol (NCP)

Sequenced packet exchange (SPX)

AppleTalk Transport Protocol (ATP)
The Transport layer also handles addressing with ports and sockets, which are addresses
that identify which upper-layer program or process is communicating on a particular
device. The Transport layer can provide both connection-oriented and connectionless ser-
vices to an upper-layer protocol.
As part of the data stream sequence of the OSI, the Transport layer has the task of seg-
menting the data handed down by upper-layer applications. To govern the tracking and
management of various segments, the Transport layer uses port numbers for each applica-
tion.
This layer can be confusing to people because, when they think about the Transport layer,
they envision guaranteed, reliable transport and connection-oriented services. In fact, this
depends on what your vendor implements. If a vendor who is writing an application (an
upper-level service) wants to provide reliable transport, it will use a reliable transport pro-
tocol such as TCP in the TCP/IP suite. If that same vendor prefers speed to reliability, it
will implement a connectionless protocol at the Transport layer, such as UDP in the
TCP/IP suite.
The Transport layer, whether connection-oriented or connectionless, deals with ports,
sockets, and process addresses. Client-based and server-based addresses such as TCP and
UDP ports are used to identify the process running within a host.
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32
Ports fall into the three categories shown in Table 2.2.
Table 2.2 Port Categories
Port Description
Well-Known Ports These define well-known programs used in the industry and have become
de facto standards for addressing such programs. They fall into the range
of 0–255.
Less Well-Known These ports are reserved and can be implemented by vendors on an as-needed
basis. They range from 256–1023.
Client These are variable (or ethereal) ports available each time a client process begins
and opens a new port. The range is 1024–65535.
When you open a client session, such as a client Telnet connection, that session opens up
a unique port, which is a variable or made-up port. The connection uses this port to
reach a Telnet server. When you connect to the host or server, typically you are connect-
ing to a well-known port; for example, Telnet uses well-known port 23 (see Figure 2.6).
Figure 2.6
Client ports are randomly selected, whereas server processes use well-known ports.
Your client and your server port clearly identify which process on each box is communi-
cating. TCP, or the connection-oriented transport protocol, then maintains the connec-
tion-oriented processes. Using a connectionless protocol, such as UDP, you would simply
pass data unreliably and hope that it gets to its destination while relying on other proto-
cols to maintain the connection.
Key Concept
It’s important to note that this layer deals with sockets or port addresses. TCP
and UDP ports identify the process or program running within a host.
Client and Well-Known Ports
Telnet Server
Port 23
Client Port
4001
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General Description of OSI Layers
Network Layer
The primary responsibility of the Network layer is to determine the best path for routing
data between networks.
The Network layer covers the following:

Connectionless protocols

End-to-end communication between two hosts

Logical addressing

Packet delivery

Routing
The Network layer has no connection-oriented protocols.
To achieve the best routing of data, the Network layer utilizes packet switching, a process
by which the router addresses traffic received in one interface and then sends it out on a
different interface to its destination.
Network layer protocols deal with logical addressing, which is distinguished from the
Physical layer MAC (Media Access Control) address associated with a network card.
Unlike physical addresses, logical addresses are not permanently assigned; instead, they are
assigned by an administrator, either manually or dynamically.
Each logical address consists of two parts, which identify where it belongs:

The Network Address—This address makes routing possible by directing the traf-
fic toward the best path to its destination.

The Node Address—This address belongs to the originating node or the destina-
tion node.
Addressing in Novell’s IPX and Apple’s Datagram Delivery Protocol (DDP) follow similar
conventions as IP addressing. Both are divided in a hierarchical fashion into a network
portion and a node portion, and the addresses within each group cannot be separated by
a router. IPX addresses consist of 10 bytes, the first 4 of which represent the network por-
tion of the address and the last 6 of which represent the node portion. One advantage to
IPX addressing is that the node portion of the address is always assigned automatically,
easing administration. AppleTalk addresses, on the other hand, use a longer 24-bit
address, with the first 16 bits representing the network portion and the last 8 bits repre-
senting the node portion of the address.
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Chapter 2 • Overview of Industry Models and Standards
34
Key Concept
The Network layer also encompasses fragmentation and reassembly. Although
these functions occur (in the real world) at the Network layer (as performed by IP
or IPX), Cisco prefers that you associate them with the Transport layer.
Fragmentation and Reassembly
Data frames that exceed the legal size of network media you are accessing must always be
broken down into manageable portions during transmission. Even though the object is
supposed to maximize the amount of data sent over the media, any frame deemed too
large for any medium on the network automatically undergoes fragmentation to reduce
the frame to an acceptable size. In any given network, the maximum frame size can only
equal the capacity of the smallest routing medium.
Network media that can handle larger frames have the advantage of saving overhead,
CPU cycles, and time. Conversely, if a router must break down the transmission, the
result is added time and latency.
At the receiving end of the transmission, the destination host reassembles the data and
passes it up to the higher layers.
For example, if you attempt to send 1MB of data over the wire in a system that accom-
modates a maximum transmission unit (MTU) of 512KB through any piece of its media,
you would, in theory, overwhelm the system. As a result, the routers fragment the data
into frames no larger than 512KB while transmitting to the host receiver (see Figure 2.7).
When the data arrives, the host reassembles it into its total framework and sends it to the
next higher layer of the OSI.
The Network layer protocols include

IP, IPX—Protocols that deal with logical network addresses

RARP, ARP, BootP, and DHCP—Protocols that perform address resolution or
configuration

ICMP—Diagnostic and control protocol

RIP and OSPF—Routers and routing protocols
Routers use logical addressing from a source and destination to ensure that data is passed
from one network to another. Routing protocols also function at the Network layer.
OSPF is a link state protocol that also can provide routing services.
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General Description of OSI Layers
Figure 2.7
Routers can perform fragmentation if necessary.
Data Link Layer
The OSI Data Link layer’s function is to send and receive data over the wire, as well as
identify what upper-layer protocol is being carried within a frame.
The Data Link layer adds both a header at the front and a four-byte trailer at the end of
each frame prior to transmission, thereby forming a frame around the data. The term
packet framing refers to the formation of such frame sequences. The Data Link layer is the
only one that adds a trailer to the data.
The Data Link layer performs the following:

Controls access to the medium

Adds source and destination hardware addresses

Prepares frames for transmission by converting data packets to frames

Assumes the function of sending and receiving data over the wire

Calculates CRC or FCS
Data Link Addresses
For data to be delivered reliably across networks, each device sending and receiving data
must have a unique address. Unique addresses ensure that the data being sent arrives at its
intended destination. The OSI Reference Model contains two definitions for station
256
256
256
256
256
256
256
Fragmentation and Reassembly
R1
R3
R2
A
B
1518
1518
256
256
256
MTU=1518 bytes
MTU=1518 bytes
X.25 Network
MTU=256 bytes+
256
256
1518
MTU=256 bytes
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Chapter 2 • Overview of Industry Models and Standards
36
addresses: the network address and data link address (also known as MAC address). MAC
addresses exist within the Data Link layer, and layer-2 devices, such as switches and
bridges, use these addresses to forward frames.
The MAC sublayer of the Data Link layer serves as the conduit to the Physical layer and
physical media. The MAC is also synonymous with the physical address on the network
card.
The term media access, from which the MAC protocol takes its name, describes the
method of converting data—received as 1s and 0s—from the Physical layer. Different
network topologies use one of three channel access methods governing how devices
access, transmit, and then release a channel. Table 2.3 illustrates the methods and the
topologies that use them.
Table 2.3 Channel Access Methods
Method Description Topology
Contention Demands that a given Bus
machine be the only
one trying to transmit
at a given moment to
avoid data collision.
Devices “contend” for
the right to transmit.
Token Passing A machine wishing to Ring
transmit must receive
a “token” frame for
the right to transmit.
This prevents
collisions because only
one medium can transmit
at a time.
Polling A master or primary Mainframe and Mini
regularly polls all Environments
machines, called
secondaries or
slaves, on the
network to ask whether
they want to transmit.
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General Description of OSI Layers
Layer 2 Addresses
Data link addresses or MAC addresses are physically burned-in addresses on each network