Wiley the all new switch book the complete guide to LAN switching technology 2nd edition aug 2008 ISBN 0470287152 pdf

Seifert ffirs.tex

V3 - 06/28/2008

The All-New
Switch Book
The Complete Guide to LAN
Switching Technology
Second Edition
Rich Seifert
Jim Edwards

Wiley Publishing, Inc.

10:03am

Page iii


Seifert

ffirs.tex

V3 - 06/28/2008

The All-New
Switch Book

10:03am

Page i


Seifert

ffirs.tex

V3 - 06/28/2008

10:03am

Page ii


Seifert ffirs.tex

V3 - 06/28/2008

The All-New
Switch Book
The Complete Guide to LAN
Switching Technology
Second Edition
Rich Seifert
Jim Edwards

Wiley Publishing, Inc.

10:03am

Page iii


Seifert ffirs.tex

V3 - 06/28/2008

The All-New Switch Book: The Complete Guide to LAN Switching Technology,
Second Edition
Published by
Wiley Publishing, Inc.
10475 Crosspoint Boulevard
Indianapolis, IN 46256
www.wiley.com

Copyright © 2008 by Rich Seifert and Jim Edwards
Published by Wiley Publishing, Inc., Indianapolis, Indiana
Published simultaneously in Canada
ISBN: 978-0-470-28715-6
Manufactured in the United States of America
10 9 8 7 6 5 4 3 2 1
No part of this publication may be reproduced, stored in a retrieval system or transmitted
in any form or by any means, electronic, mechanical, photocopying, recording, scanning or
otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright
Act, without either the prior written permission of the Publisher, or authorization through
payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood
Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600. Requests to the Publisher
for permission should be addressed to the Legal Department, Wiley Publishing, Inc., 10475
Crosspoint Blvd., Indianapolis, IN 46256, (317) 572-3447, fax (317) 572-4355, or online at
/>Limit of Liability/Disclaimer of Warranty: The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of

this work and specifically disclaim all warranties, including without limitation warranties
of fitness for a particular purpose. No warranty may be created or extended by sales or
promotional materials. The advice and strategies contained herein may not be suitable for
every situation. This work is sold with the understanding that the publisher is not engaged
in rendering legal, accounting, or other professional services. If professional assistance is
required, the services of a competent professional person should be sought. Neither the
publisher nor the author shall be liable for damages arising herefrom. The fact that an
organization or Website is referred to in this work as a citation and/or a potential source of
further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further,
readers should be aware that Internet Websites listed in this work may have changed or
disappeared between when this work was written and when it is read.
For general information on our other products and services or to obtain technical support,
please contact our Customer Care Department within the U.S. at (800) 762-2974, outside the
U.S. at (317) 572-3993 or fax (317) 572-4002.
Library of Congress Cataloging-in-Publication Data is available from the publisher.
Trademarks: Wiley, the Wiley logo, and are trademarks or registered trademarks of John
Wiley & Sons, Inc. and/or its affiliates in the United States and other countries, and may
not be used without written permission. All other trademarks are the property of their
respective owners. Wiley Publishing, Inc., is not associated with any product or vendor
mentioned in this book.
Wiley also publishes its books in a variety of electronic formats. Some content that appears
in print may not be available in electronic books.

10:03am

Page iv


Seifert ffirs.tex

V3 - 06/28/2008

10:03am

To my granddaughter, Annaliese Grace. May she enjoy all of the
happiness that life has to offer. I am looking forward to all of the things
that she will be teaching me for the many years to come.
— Jim Edwards

Page v


Seifert ffirs.tex

V3 - 06/28/2008

10:03am

Page vi


Seifert fbetw.tex

V1 - 06/28/2008

10:04am

Credits

Executive Editor

Carol Long
Senior Development Editor
Tom Dinse
Production Editor
Rachel McConlogue
Copy Editor
Nancy Rapoport

Vice President and Executive
Group Publisher
Richard Swadley
Vice President and Executive
Publisher
Joseph B. Wikert
Project Coordinator, Cover
Lynsey Stanford
Proofreader
PubServices

Editorial Manager
Mary Beth Wakefield

Indexer
Jack Lewis

Production Manager
Tim Tate

Cover Image
© Jupiter Images

vii

Page vii


Seifert

fbetw.tex

V1 - 06/28/2008

10:04am

Page viii


Seifert

ftoc.tex

V1 - 06/28/2008

10:05am

Contents

Preface

xxiii

Introduction

xxv

Part One

Foundations of LAN Switches

Chapter 1

Laying the Foundation
Network Architecture
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
Layering Makes a Good Servant but a Bad Master
Inside the Data Link Layer
Modes of Operation
Data Link Sublayering
Logical Link Control
Addressing
Local and Global Uniqueness
LAN Data Link Addresses
Unicast and Multicast Addresses
Globally Unique and Locally Unique MAC Addresses

How LAN Addresses Are Assigned
Written Address Conventions
LAN Technology Review
Ethernet

3
4
5
6
7
7
8
8
9
9
12
12
15
16
19
19
20
21
23
24
26
27
27

ix

Page ix


Seifert ftoc.tex

x

V1 - 06/28/2008

Contents
Ethernet Medium Access Control
Ethernet Physical Layer Options and Nomenclature
Ethernet Frame Formats
Bit-Ordering
Token Ring
Token Ring Medium Access Control
Token Ring Physical Layer Options
Token Ring Frame Formats
Bit-Ordering on Token Ring LANs
Fiber Distributed Data Interface
FDDI Operation
FDDI Physical Signaling
FDDI Frame Format
Other LAN Technologies

Chapter 2

28
31

33
38
38
39
41
41
43
43
43
45
45
46

IEEE LAN Standards
IEEE 802 Organization
IEEE 802 Naming Conventions, or ’’Mind Your Ps and Qs’’
IEEE 802.1
IEEE 802.3
IEEE 802.5
Other Standards Organizations
Terminology
Applications, Clients, and Service Providers
Encapsulation
Stations and Interconnections

48
49
50
51
53

54
54
55
56
57
59

Transparent Bridges
Principles of Operation
Unicast Operation
Unknown and Multicast Destinations
Generating the Address Table
Address Table Aging
Process Model of Table Operation
Custom Filtering and Forwarding
Multiple Bridge Topologies
Transparent Bridge Architecture
Maintaining the Link Invariants
The Hard Invariants Are Hard Indeed
Soft Invariants
Implementing the Bridge Address Table
Table Operations
Search Algorithms
Hash Tables
Binary Search
Content-Addressable Memories
How Deep Is Your Table?
Aging Entries from the Table

63

63
65
66
68
69
70
72
73
74
76
78
80
84
85
85
85
88
90
92
93

10:05am

Page x


Seifert

ftoc.tex

V1 - 06/28/2008

10:05am

Contents
Bridge Performance
What Does It Take to Be the Best?
If You’re Not the Best, How Good Are You?
The IEEE 802.1D Standard
Operating Parameters and Requirements
Aging Time
Bridge Transit Delay
Additional Operating Requirements
Bridge Address Assignment
Reserved Addresses

95
95
97
98
99
99
99
101
102
103

Chapter 3

Bridging Between Technologies

Bridging the LAN Gap
LAN Operational Mechanisms
Frame Format Translation
MAC-Specific Fields
User Data Encapsulation
Translating Versus Encapsulating Bridges
Issues in Bridging Dissimilar LANs
Maximum Transmission Unit (MTU)
Frame Check Protection
Bit-Ordering
Functional Groups Versus True Multicast Addressing
LAN-Specific Features
Thoughts on Bridging Dissimilar LANs
Bridging Between Local and Wide Area Networks
Applications of Remote Bridges
Technologies for Remote Bridges
Encapsulation
Issues in Remote Bridges
Error Rate
LAN Bandwidth and Delay
IEEE 802.1G — Not!

105
106
107
108
109
110
115
117

117
124
126
131
133
137
137
138
139
141
143
143
144
145

Chapter 4

Principles of LAN Switches
A Switch Is a Bridge Is a Switch
Switched LAN Concepts
Separate Access Domains
Segmentation and Microsegmentation
Extended Distance Limitations
Increased Aggregate Capacity
Data Rate Flexibility
Cut-Through Versus Store-and-Forward Operation
MultiLayer Switching
Layer 3 Switching
A Router by Any Other Name Would
Still Forward Packets

147
147
148
149
150
152
152
153
153
158
159
160

xi

Page xi


Seifert

xii

ftoc.tex

V1 - 06/28/2008

Contents
Layer 3 Switch Operation
Layer 4 Switching

Chapter 5

162
173

A Switch Is a Switch Is a Switch Except When ...
Four Generations of Switch Integration
Switch Configurations
Bounded Systems
Stackable Switches
Stacking the Deck
A Block in the Ointment
United, We Are One
Chassis Switches
Switch Application Environments
Desktop Level
Workgroup Level
Campus Level
Enterprise Level
The Needs Change with the Level
Numbers of Ports
Layer 2 Versus Layer 3 Switching
(Bridging Versus Routing)
Table sizes
Link Technologies
Port Data Rates and Aggregate Capacity
Media Support

176

177
182
183
184
184
185
185
187
188
190
190
191
191
192
192

Loop Resolution
Diary of a Loopy LAN
Getting Yourself in the Loop
Getting out of the Loop
The Spanning Tree Protocol
History of the Spanning Tree Protocol
Spanning Tree Protocol Operation
Spanning Tree Protocol Concepts
Calculating and Maintaining the Spanning Tree
Bridge Protocol Data Units
Port States
Topology Changes
Protocol Timers
Issues in STP Implementation

Queuing of BPDUs Relative to Data
Save a Receive Buffer for Me!
Spanning Tree Protocol Performance
Rapid Spanning Tree Protocol
RSTP State of the Port Address
Discarding
Learning
Forwarding

201
201
203
204
205
205
206
207
213
217
220
222
224
226
227
227
228
229
229
230
230

231

195
196
198
198
199

10:05am

Page xii


Seifert

ftoc.tex

V1 - 06/28/2008

10:05am

Contents
Port Roles
The Root Port
The Designated Port
The Alternate Port
The Backup Port
Forwarding State — Rapid Transition
Edge Port
Link Type

BPDUs (Bip-A-Doo-Two)
BPDU — The Final Frontier ...er ... uh ... The New Format
How It Is Now Handled
Multiple Spanning Tree Protocol
RSTP, MSTP, and STP (Can’t we all just get along?)

Chapter 6

231
231
232
232
232
234
234
234
234
234
235
236
236

Loops in a Remotely Bridged (WAN) Catenet
There’s More Than a One-Letter Difference
Spanning Tree on a WAN
Link Utilization
Delay
Using a Single Path for All Traffic
Proprietary Loop Resolution Algorithms
Routing Versus Bridging on the WAN

An Example of Loop Resolution
Behavior of a Spanning Tree Catenet
Maintaining the Link Invariants
Data Flow on the Spanning Tree
Traffic Congregation at the Root
Topology Changes and Disruption
Configuring the Spanning Tree
‘‘We’ll All Be Planning That Root ...’’
Assigning Link Costs
Setting Protocol Timers
Managing the Extent of the Catenet
Up a Tree Without a Protocol?
Why Would Anyone Do This?
Interoperability
What to Do, What to Do?

237
238
238
239
239
239
241
242
242
245
246
246
248
248

248
249
250
250
251
252
252
253
253

Source Routing
Overview of Source Routing Operation
Eine Kleine Sourceroutinggeschichte
Source Routing Concepts
Nontransparency, or ‘‘Peek-a-Boo — I See You!’’
Who’s the Boss?
Connection Orientation
Be All That You Can Be (Without Joining the Army)
Even Token Rings Need to Get Out of the Loop Sometimes
Ring and Bridge Numbering

255
256
257
259
260
260
261
263
263

264

xiii

Page xiii


Seifert ftoc.tex

xiv

V1 - 06/28/2008

Contents
Route Discovery
Maximum Transmission Unit Discovery

Source-Routed Frames
Differentiating Source-Routed and
Non-Source–Routed Frames
Non-Source–Routed Frames
Source-Routed Frame Format
Routing Control Fields
Route Descriptors
Source Routing Operation
Route Discovery
Route Discovery Algorithms
Route Discovery Frames
Route Selection
Issues in Route Discovery

Station Operation
Architectural Model of Source Routing
End Station Transmit Behavior
End Station Receive Behavior
Bridge Operation
Bridge Behavior for Specifically Routed Frames
Bridge Behavior for Explorer Frames (Both ARE and STE)
Interconnecting the Source-Routed and
Transparently Bridged Universes
Don’t Bridge — Route!
The Source Routing-to-Transparent Bridge
The Source Routing/Transparent Bridge
IEEE Standards and Source Routing
The Future of Source Routing
Part Two
Chapter 7

Advanced LAN Switch Concepts
Full Duplex Operation
Why a MAC?
Full Duplex Enablers
Dedicated Media
Dedicated LAN
Full Duplex Ethernet
‘‘Ethernet Is CSMA/CD’’
Full Duplex Ethernet Operating Environment
Subset of Half Duplex Operation
Transmitter Operation
Receiver Operation
Ethernet Minimum Frame Size Constraint

Dedicated Token Ring
Implications of Full Duplex Operation
Eliminating the Link Length Restriction of
Half Duplex Ethernet

266
266

267
267
269
269
269
273

274
275
275
277
279
280
282
282
282
284
285
286
286
289
294

295
298
301
301
305
305
307
307
310
311
312
313
314
315
315
316
317
319
319

10:05am

Page xiv


Seifert ftoc.tex

V1 - 06/28/2008

10:05am

Contents
Increasing the Link Capacity
Increasing Switch Load

320
322

Full Duplex Application Environments
Switch-to-Switch Connections
Server and Router Connections
Long-Distance Connections

323
323
324
325

Chapter 8

LAN and Switch Flow Control
The Need for Flow Control
Default Switch Behavior
The Effect of Frame Loss
End-to-End Flow Control
Cost-Performance Tradeoffs
Controlling Flow in Half Duplex Networks
Backpressure
Aggressive Transmission Policies
MAC Control

MAC Control Architecture
MAC Control Frame Format
PAUSE Function
Overview of PAUSE Operation
PAUSE Frame Semantics
Configuration of Flow Control Capabilities
IEEE 802.3x Flow Control Implementation Issues
Design Implications of PAUSE Function
Inserting PAUSE Frames in the Transmit Queue
Parsing Received PAUSE Frames
PAUSE Timing
Buffering Requirements
Flow Control Policies and Use
Buffer Thresholds
Selection of PAUSE Times
Dealing with Unreliable Delivery
Flow Control Symmetry
Symmetric Flow Control
Asymmetric Flow Control

327
327
330
330
332
332
333
333
337
341

341
343
344
346
347
349
350
351
351
352
353
354
356
356
357
358
358
359
359

Chapter 9

Link Aggregation
Link Aggregation Benefits
Application of Link Aggregation
Switch-to-Switch Connections
Switch-to-Station (Server or Router) Connections
Station-to-Station Connections
Aggregate or Upgrade?
Issues in Link Aggregation

Addressing
Distributing Traffic Across an Aggregation

361
362
364
365
365
367
367
368
368
371

xv

Page xv


Seifert ftoc.tex

xvi

V1 - 06/28/2008

Contents
Maintaining Link Invariants in an
Aggregated Environment
Separating Traffic Flows
Conversation Determination Aids

the Realization of Aggregation
Mapping the Distribution Function to the Physical Link
Conversations Above the Data Link Layer
Summary of Distribution Functions
Changing the Distribution
Performance
Technology Constraints (a.k.a. Link Aggravation)
Mixing LAN Technologies in a Single Aggregation
Mixing Data Rates in a Single Aggregation
Aggregation and Shared LANs
Configuration Control

IEEE 802.3ad Link Aggregation Standard
Scope of the Standard
Features and Benefits of the Standard
Link Aggregation Architectural Model
Binding Physical Ports to Aggregators
Binding, Distribution, and Collection
Addressing
Marker Protocol Operation
Link Aggregation Control Protocol
LACP Concepts
LACP Frame Format
Split Up the Trunk

372
374
375
377
377

380
381
384
384
384
385
385
385

388
388
390
392
394
397
397
398
401
401
406
410

Chapter 10 Multicast Pruning
Multicast Usage
Who Assigns Multicast Addresses?
Application Use of Multicast
Implications of Default Behavior
Trimming the (Spanning) Tree
The Weekend Networker’s Guide to Tree Pruning
Receiver Declaration

Registration of the Declaration
Propagation of the Registration
Source Pruning
IEEE 802.1p
GARP Multicast Registration Protocol
Generic Attribute Registration Protocol
GMRP Use of GARP

413
413
414
417
419
420
421
421
422
423
424
424
424
426
430

Chapter 11 Virtual LANs: Applications and Concepts
Applications of VLANs
The Software Patch Panel
LAN Security

433

434
434
437

10:05am

Page xvi


Seifert ftoc.tex

V1 - 06/28/2008

10:05am

Contents
User Mobility
Bandwidth Preservation

VLAN Concepts
Playing Tag on Your LAN
Implicit Tags
Explicit Tags
VLAN Awareness and Tag Awareness
VLAN Awareness
What It Means to Be VLAN-Aware
VLAN-Aware Switches
VLAN-Aware End Stations
He Looks Around, Around, He Sees VLANs in the
Architecture, Spinning in Infinity...

Shared Media and VLAN Awareness
Non–VLAN-Aware Switches and End Stations
VLAN Association Rules (Mapping Frames to VLANs)
Port-Based VLAN Mapping
MAC Address-Based VLAN Mapping
Protocol-Based VLAN Mapping
IP Subnet-Based VLAN Mapping
A VLAN Phenomenon: The One-Armed Router
Application-Based VLAN Mapping
The Rules Follow the Application
Frame Forwarding
Chapter 12 Virtual LANs: The IEEE Standard
Overview and Scope of the Standard
Elements of the Standard
Tag and Frame Formats
VLAN Protocol Identifier
Tag Control Information Field
Embedded Routing Information Field
Route Control Portion
Route Descriptor Portion
Tagged Ethernet Frames
Flash! Ethernet MTU Increases by 4 Bytes!
Tagged Token Ring Frames
Tagged FDDI Frames
VLAN Tags on Other LAN Technologies
A Word on Bit and Byte Order
IEEE 802.1Q Switch Operation
Ingress Process
Acceptable Frame Filter
Ingress Rules

Ingress Filter
Progress Process
Forwarding in a VLAN-Aware Switch

439
442

443
445
445
446
448
448
449
449
454
456
458
458
459
460
461
462
465
466
469
471
472

475

477
478
480
481
482
485
486
487
488
492
495
495
496
496
497
499
499
499
500
500
500

xvii

Page xvii


Seifert

ftoc.tex

V1 - 06/28/2008

xviii Contents
Maintaining the Filtering Database
Egress Process
Egress Rules
Egress Filter
System-Level Switch Constraints
GARP VLAN Registration Protocol
GVRP Use of GARP

Multicast Registration and VLAN Context
VLANs and the Spanning Tree
The Multiple Spanning Tree Protocol
So Exactly What Are They Trying to Accomplish Here?
What the Heck Does This All Mean?
Tha-tha-tha-tha-tha...That’s Right Folks!
Multiple Spanning Tree Instance
MST Regions

501
502
502
504
506
506
507

508

508
511
511
512
512
513
514

Chapter 13 Priority Operation
Why Priority?
LAN Priority Mechanisms
Token Ring Priority Mechanisms
FDDI Priority Mechanisms
Ethernet Priority Mechanisms
VLAN and Priority Tagging
Getting into the Priority Business
Priority Operation in Switches
The Ordering Invariant — Redux
IEEE 802.1p
Switch Process Flow for Priority Operation
Determining Frame Priority on Input
Tag, You’re It!
LAN-Specific User Priority Indication
Implicit Priority Determination, or
‘‘Whose Clues Do You Use?’’
Priority Regeneration
Mapping Input Priority to Class-of-Service
Class of Service Versus Quality of Service
How Many Queues Do You Chueues?
Default Priority Mappings

Output Scheduling
Scheduling Algorithms
Indicating the Priority in Transmitted Frames
Mapping User Priority to Access Priority
at the Output Port

517
517
519
520
521
522
525
526
529
530
530
532
533
533
533

Chapter 14 LAN Security
Network Security Overview
Hackers, Crackers, Viruses, and Those Confounded Worms
Hac and Crac, the Ker Brothers.

547
548
549

549

534
535
536
536
538
540
541
541
544
545

10:05am

Page xviii


Seifert ftoc.tex

V1 - 06/28/2008

10:05am

Contents
Malware
Physical Security
Proactive Measures
Virus Containment
Firewalls

End User Checks and Balances

LAN Security
Security Concerns at Layer 2
Man in the Middle
MAC Address Table Flooding
DHCP Attacks
Spanning Tree Attacks
Private VLAN Attack
VLAN Migration (Hopping) Attack
ARP Spoofing Attack
Wrap Up
Chapter 15 Switch Management
The Simple Network Management Protocol
SNMP Concepts
Manager/Agent Architecture
Management Information Base
The Simple Network Management Protocol
The Simple Network Management Protocol Version 2
The Simple Network Management Protocol Version 3
Network Monitoring Tools
Protocol Analysis in a Switched LAN
Mirror, Mirror on the Switch, Which Is the Port
That’s Got the Glitch?
Switch Mirroring
Look Within Yourself for the Truth
RMON Capabilities and MIBs
Ethernet Statistics Group
Ethernet History Group
Alarm Group

Host Group
HostTopN Group
Matrix Group
Filter Group
Packet Capture Group
Event Group
RMON Support for Virtual LANs
Levels of RMON Support
Internal Switch Management Platforms
Non-SNMP Management
Internal Web Servers
Out-of-Band Management

550
551
552
553
553
555

555
555
557
557
559
560
561
561
563
563

565
566
568
568
569
573
575
576
577
580
581
583
585
586
586
589
590
591
594
594
596
597
597
598
598

598
601
602
602

xix

Page xix


Seifert ftoc.tex

xx

V1 - 06/28/2008

Contents
Management by Telnet
Management by Secure Shell
Reach Out and Ping Someone

604
605
607

Chapter 16 Network Troubleshooting Strategies
The Trouble with Troubleshooting
Housekeeping
Running the Network Baseline
Proactive Troubleshooting
Troubleshooting Tools
Troubleshooting Utilities
ping
trace route

netstat
route
ARP
More Advanced Tools of the Trade
Network Analyzers (or whatever
they are calling them today)
Other Testing Equipment
... and if all else fails
A Systematic Approach
Defining the Problem
Sharing the Known
Determining the Issue
Developing a Solution
Resolving and Taking Action!
Monitoring the Results
The Final Step — Have a Beer!
Some Strategies for Layer 2 Troubleshooting
Performing a Health Check
Software, Hardware, and Configuration
Issues Relating to Software
Issues Relating to Hardware
Issues Relating to Configuration
Common Layer 2 Issues
VLANS
Duplex Mismatches
Spanning Tree
Wrap Up

609
610

611
611
613
614
615
615
617
617
618
620
620

Chapter 17 Make the Switch!
Keeping House
Housekeeping Functions
Implementation and Performance
(or, It’s Tough to Find a Good Housekeeper)

641
644
645

621
622
623

624
624
625
625

626
627
627
627
628
628
629
629
630
632
632
632
633
636
637

647

10:05am

Page xx


Seifert ftoc.tex

V1 - 06/28/2008

10:05am

Contents

Switch Data Receive Path Functions
Port Interfaces (Receive)
Receive Flow Control
Link Aggregation Collector
Classification Engine
Local Sinking of Reserved Multicast Addresses
VLAN Ingress Rules
Priority Assessment
Do It Once and Save the Results
Implementation of the Classification Engine
VLAN Filters
Lookup Engine
Generating the Output Vector
Maintaining the Filtering Database
Lookup Implementation
Switch Fabrics
Shared Memory
Shared Memory Fabric Operation
Multicasting in a Shared Memory Architecture
Buffer Organization
Memory Bandwidth Limitations
Increasing the Memory Bandwidth
Shared Bus
Crosspoint Matrix
Multicasting in a Crosspoint Matrix Fabric
Crosspoint Matrix Implementation
The Head-of-Line Blocking Problem
Solving the Head-of-Line Blocking Problem
Priority Levels in the Switch Fabric
Input Versus Output Queues

Input Queues and Shared Memory Switch Fabrics
Input Queues, Output Queues, and Flow Control
Switch Data Transmit Path Functions
Output Filters
Output Queues and Priority Handling
Link Aggregation Distributor
Transmit Flow Control
Hey, Kids! What Time Is It?
Port Interfaces (Transmit)

647
647
649
650
650
651
651
653
653
655
657
658
659
662
662
665
665
665
667
668

671
672
674
677
677
679
680
682
690
690
691
691
692
692
695
696
696
697
697

Appendix: Protocol Parsing

699

References

703

Glossary

711

Index

753

xxi

Page xxi


Seifert

ftoc.tex

V1 - 06/28/2008

10:05am

Page xxii


Seifert

flast.tex

V3 - 06/28/2008

10:06am

Preface

The invasion of Local Area Networks (LANs) into the commercial, industrial,
university, and even the home environment during the 1980s and 1990s was
nothing short of phenomenal. No longer did organizations consider whether
they need a network, but only what type of network should be employed and
what devices should be used to build the network infrastructure.
Most early LANs were designed around the use of a shared communications
channel — for example, a coaxial cable bus. During the late 1980s and early
1990s, two phenomena occurred that would fundamentally change the way
that end user LANs were designed:
LAN topology migrated from the use of a shared medium to standardized structured wiring systems, implemented primarily using
unshielded twisted pair (UTP) cable and central wiring hubs.
End user computing equipment and application requirements
advanced to the point where the capacity of a shared LAN could actually
limit overall system performance.
These two factors (together with commensurate advances in silicon technology) fostered the development and deployment of LAN switches. While
traditional, shared-bandwidth wiring hubs are still in use today, they are
generally considered acceptable only at the edge of the network or when
application demands do not seriously tax LAN performance. Switches have
become almost ubiquitous for backbone interconnections. As switch prices
decreased, they became popular even for desktop use, as they can provide
performance advantages and growth capability for only a very small premium
over their non-switched counterparts.

xxiii

Page xxiii