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

Wiley Publishing, Inc.

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The All-New
Switch Book

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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
http://www.wiley.com/go/permissions.


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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

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Credits


© Jupiter Images

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Contents

Preface


Globally Unique and Locally Unique MAC Addresses
How LAN Addresses Are Assigned
Written Address Conventions
LAN Technology Review
Ethernet

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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

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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!

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Still Forward Packets

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Contents
Layer 3 Switch Operation

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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

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

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?

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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

Ethernet Minimum Frame Size Constraint
Dedicated Token Ring
Implications of Full Duplex Operation
Eliminating the Link Length Restriction of
Half Duplex Ethernet

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Contents
Increasing the Link Capacity
Increasing Switch Load

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

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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

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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?

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

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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

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


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

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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?

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Contents
Malware
Physical Security
Proactive Measures
Virus Containment

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

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

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

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

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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

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Appendix: Protocol Parsing

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References

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Glossary


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.

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