The All-New Switch Book

The Complete Guide Switching Technology

Second Edition i

Rich Seifert Jim Edwards

WILEY

Wiley Publishing, Inc.

Contents

Preface

Introduction

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

xxiii

XXV

3 4 5 6 7 7 8 8 9 9

12 12 15 16 19 19 20 21 23 24 26 27 27

ix

Contents

Ethernet Medium Access Control 28 Ethernet Physical Layer Options and Nomenclature 31 Ethernet Frame Formats 33 Bit-Ordering 38

Token Ring 38 Token Ring Medium Access Control 39 Token Ring Physical Layer Options 41 Token Ring Frame Formats 41 Bit-Ordering on Token Ring LANs 43

Fiber Distributed Data Interface 43 FDDI Operation 43 FDDI Physical Signaling 45 FDDI Frame Format 45

Other LAN Technologies 46 IEEE LAN Standards 48

IEEE 802 Organization 49 IEEE 802 Naming Conventions, or "Mind Your Ps and Qs" 50 IEEE 802.1 51 IEEE 802.3 53 IEEE 802.5 54 Other Standards Organizations 54

Terminology 55 Applications, Clients, and Service Providers 56 Encapsulation 57 Stations and Interconnections 59

Chapter 2 Transparent Bridges 63 Principles of Operation 63

Unicast Operation 65 Unknown and Multicast Destinations 66 Generating the Address Table 68 Address Table Aging 69 Process Model of Table Operation 70 Custom Filtering and Forwarding 72 Multiple Bridge Topologies 73

Transparent Bridge Architecture 74 Maintaining the Link Invariants 76

The Hard Invariants Are Hard Indeed 78 Soft Invariants 80

Implementing the Bridge Address Table 84 Table Operations 85 Search Algorithms 85

Hash Tables 85 Binary Search 88 Content-Addressable Memories 90

How Deep Is Your Table? 92 Aging Entries from the Table 93

Contents xi

Bridge Performance 95 What Does It Take to Be the Best? 95 If You're Not the Best, How Good Are You? 97

The IEEE 802.1D Standard 98 Operating Parameters and Requirements 99

Aging Time 99 Bridge Transit Delay 99 Additional Operating Requirements 101

Bridge Address Assignment 102 Reserved Addresses 103

Chapter 3 Bridging Between Technologies 105 Bridging the LAN Gap 106

LAN Operational Mechanisms 107 Frame Format Translation 108

MAC-Specific Fields 109 User Data Encapsulation 110 Translating Versus Encapsulating Bridges 115

Issues in Bridging Dissimilar LANs 117 Maximum Transmission Unit (MTU) 117 Frame Check Protection 124 Bit-Ordering 126 Functional Groups Versus True Multicast Addressing 131 LAN-Specific Features 133

Thoughts on Bridging Dissimilar LANs 137 Bridging Between Local and Wide Area Networks 137

Applications of Remote Bridges 138 Technologies for Remote Bridges 139 Encapsulation 141 Issues in Remote Bridges 143

Error Rate 143 LAN Bandwidth and Delay 144

IEEE 802.1G —Not! 145

Chapter 4 Principles of LAN Switches 147 A Switch Is a Bridge Is a Switch 147 Switched LAN Concepts 148

Separate Access Domains 149 Segmentation and Microsegmentation 150 Extended Distance Limitations 152 Increased Aggregate Capacity 152 Data Rate Flexibility 153

Cut-Through Versus Store-and-Forward Operation 153 MultiLayer Switching 158

Layer 3 Switching 159 A Router by Any Other Name Would

Still Forward Packets 160

xii Contents

Layer 3 Switch Operation 162 Layer 4 Switching 173

A Switch Is a Switch Is a Switch Except When ... 176 Four Generations of Switch Integration 177 Switch Configurations 182

Bounded Systems 183 Stackable Switches 184

Stacking the Deck 184 A Block in the Ointment 185 United, We Are One 185

Chassis Switches 187 Switch Application Environments 188

Desktop Level 190 Workgroup Level 190 Campus Level 191 Enterprise Level 191 The Needs Change with the Level 192

Numbers of Ports 192 Layer 2 Versus Layer 3 Switching

(Bridging Versus Routing) 195 Table sizes 196 Link Technologies 198 Port Data Rates and Aggregate Capacity 198 Media Support 199

Chapter 5 Loop Resolution 201 Diary of a Loopy LAN 201

Getting Yourself in the Loop 203 Getting out of the Loop 204

The Spanning Tree Protocol 205 History of the Spanning Tree Protocol 205 Spanning Tree Protocol Operation 206

Spanning Tree Protocol Concepts 207 Calculating and Maintaining the Spanning Tree 213 Bridge Protocol Data Units 217 Port States 220 Topology Changes 222 Protocol Timers 224

Issues in STP Implementation 226 Queuing of BPDUs Relative to Data 227 Save a Receive Buffer for Me! 227 Spanning Tree Protocol Performance 228

Rapid Spanning Tree Protocol 229 RSTP State of the Port Address 229

Discarding 230 Learning 230 Forwarding 231

Contents xiii

Chapter 6

Port Roles 231 The Root Port 231 The Designated Port 232 The Alternate Port 232 The Backup Port 232

Forwarding State — Rapid Transition 234 Edge Port 234 Link Type 234

BPDUs (Bip-A-Doo-Two) 234 BPDU — The Final Frontier ...er ... uh ... The New Format 234 How It Is Now Handled 235

Multiple Spanning Tree Protocol 236 RSTP, MSTP, and STP (Can't we all just get along?) 236

Loops in a Remotely Bridged (WAN) Catenet 237 There's More Than a One-Letter Difference 238 Spanning Tree on a WAN 238

Link Utilization 239 Delay 239 Using a Single Path for All Traffic 239

Proprietary Loop Resolution Algorithms 241 Routing Versus Bridging on the WAN 242

An Example of Loop Resolution 242 Behavior of a Spanning Tree Catenet 245

Maintaining the Link Invariants 246 Data Flow on the Spanning Tree 246 Traffic Congregation at the Root 248 Topology Changes and Disruption 248

Configuring the Spanning Tree 248 "We'll All Be Planning That Root..." 249 Assigning Link Costs 250 Setting Protocol Timers 250 Managing the Extent of the Catenet 251

Up a Tree Without a Protocol? 252 Why Would Anyone Do This? 252 Interoperability 253 What to Do, What to Do? 253

Source Routing 255 Overview of Source Routing Operation 256 Eine Kleine Sourceroutinggeschichte 257 Source Routing Concepts 259

Nontransparency, or "Peek-a-Boo — I See You!" 260 Who's the Boss? 260 Connection Orientation 261 Be All That You Can Be (Without Joining the Army) 263 Even Token Rings Need to Get Out of the Loop Sometimes 263 Ring and Bridge Numbering 264

xiv Contents

Route Discovery 266 Maximum Transmission Unit Discovery 266

Source-Routed Frames 267 Differentiating Source-Routed and

Non-Source-Routed Frames 267 Non-Source-Routed Frames 269 Source-Routed Frame Format 269

Routing Control Fields 269 Route Descriptors 273

Source Routing Operation 274 Route Discovery 275

Route Discovery Algorithms 275 Route Discovery Frames 277 Route Selection 279 Issues in Route Discovery 280

Station Operation 282 Architectural Model of Source Routing 282 End Station Transmit Behavior 282 End Station Receive Behavior 284

Bridge Operation 285 Bridge Behavior for Specifically Routed Frames 286 Bridge Behavior for Explorer Frames (Both ARE and STE) 286

Interconnecting the Source-Routed and Transparently Bridged Universes 289

Don't Bridge — Route! 294 The Source Routing-to-Transparent Bridge 295 The Source Routing/Transparent Bridge 298

IEEE Standards and Source Routing 301 The Future of Source Routing 301

Part Two Advanced LAN Switch Concepts Chapter 7 Full Duplex Operation 305

Why a MAC? 305 Full Duplex Enablers 307

Dedicated Media 307 Dedicated LAN 310

Full Duplex Ethernet 311 "Ethernet Is CSMA/CD" 312 Full Duplex Ethernet Operating Environment 313 Subset of Half Duplex Operation 314 Transmitter Operation 315 Receiver Operation 315 Ethernet Minimum Frame Size Constraint 316

Dedicated Token Ring 317 Implications of Full Duplex Operation 319

Eliminating the Link Length Restriction of Half Duplex Ethernet 319

Contents xv

Increasing the Link Capacity 320 Increasing Switch Load 322

Full Duplex Application Environments 323 Switch-to-Switch Connections 323 Server and Router Connections 324 Long-Distance Connections 325

Chapter 8 LAN and Switch Flow Control 327 The Need for Flow Control 327

Default Switch Behavior 330 The Effect of Frame Loss 330 End-to-End Flow Control 332 Cost-Performance Tradeoffs 332

Controlling Flow in Half Duplex Networks 333 Backpressure 333

Aggressive Transmission Policies 337 MAC Control 341

MAC Control Architecture 341 MAC Control Frame Format 343

PAUSE Function 344 Overview of PAUSE Operation 346 PAUSE Frame Semantics 347 Configuration of Flow Control Capabilities 349

IEEE 802.3x Flow Control Implementation Issues 350 Design Implications of PAUSE Function 351

Inserting PAUSE Frames in the Transmit Queue 351 Parsing Received PAUSE Frames 352 PAUSE Timing 353 Buffering Requirements 354

Flow Control Policies and Use 356 Buffer Thresholds 356 Selection of PAUSE Times 357 Dealing with Unreliable Delivery 358

Flow Control Symmetry 358 Symmetric Flow Control 359 Asymmetric Flow Control 359

Chapter 9 Link Aggregation 361 Link Aggregation Benefits 362 Application of Link Aggregation 364

Switch-to-Switch Connections 365 Switch-to-Station (Server or Router) Connections 365 Station-to-Station Connections 367

Aggregate or Upgrade? 367 Issues in Link Aggregation 368

Addressing 368 Distributing Traffic Across an Aggregation 371

xvi Contents

Maintaining Link Invariants in an Aggregated Environment 372

Separating Traffic Flows 374 Conversation Determination Aids

the Realization of Aggregation 375 Mapping the Distribution Function to the Physical Link 377 Conversations Above the Data Link Layer 377 Summary of Distribution Functions 380 Changing the Distribution 381

Performance 384 Technology Constraints (a.k.a. Link Aggravation) 384

Mixing LAN Technologies in a Single Aggregation 384 Mixing Data Rates in a Single Aggregation 385 Aggregation and Shared LANs 385

Configuration Control 385 IEEE 802.3ad Link Aggregation Standard 388

Scope of the Standard 388 Features and Benefits of the Standard 390 Link Aggregation Architectural Model 392 Binding Physical Ports to Aggregators 394 Binding, Distribution, and Collection 397 Addressing 397 Marker Protocol Operation 398 Link Aggregation Control Protocol 401

LACP Concepts 401 LACP Frame Format 406

Split Up the Trunk 410

Chapter 10 Multicast Pruning 413 Multicast Usage 413

Who Assigns Multicast Addresses? 414 Application Use of Multicast 417 Implications of Default Behavior 419

Trimming the (Spanning) Tree 420 The Weekend Networker's Guide to Tree Pruning 421

Receiver Declaration 421 Registration of the Declaration 422 Propagation of the Registration 423 Source Pruning 424

IEEE 802.1p 424 GARP Multicast Registration Protocol 424

Generic Attribute Registration Protocol 426 GMRP Use of GARP 430

Chapter 11 Virtual LANs: Applications and Concepts 433 Applications of VLANs 434

The Software Patch Panel 434 LAN Security 437

Contents xvii

User Mobility 439 Bandwidth Preservation 442

VLAN Concepts 443 Playing Tag on Your LAN 445

Implicit Tags 445 Explicit Tags 446 VLAN Awareness and Tag Awareness 448

VLAN Awareness 448 What It Means to Be VLAN-Aware 449 VLAN-A ware Switches 449 VLAN-Aware End Stations 454 He Looks Around, Around, He Sees VLANs in the

Architecture, Spinning in Infinity... 456 Shared Media and VLAN Awareness 458 Non-VLAN-Aware Switches and End Stations 458

VLAN Association Rules (Mapping Frames to VLANs) 459 Port-Based VLAN Mapping 460 MAC Address-Based VLAN Mapping 461 Protocol-Based VLAN Mapping 462 IP Subnet-Based VLAN Mapping 465 A VLAN Phenomenon: The One-Armed Router 466 Application-Based VLAN Mapping 469 The Rules Follow the Application 471

Frame Forwarding 472

Chapter 12 Virtual LANs: The IEEE Standard 475 Overview and Scope of the Standard 477 Elements of the Standard 478 Tag and Frame Formats 480

VLAN Protocol Identifier 481 Tag Control Information Field 482 Embedded Routing Information Field 485

Route Control Portion 486 Route Descriptor Portion 487

Tagged Ethernet Frames 488 Flash! Ethernet MTU Increases by 4 Bytes! 492 Tagged Token Ring Frames 495 Tagged FDDI Frames 495 VLAN Tags on Other LAN Technologies 496 A Word on Bit and Byte Order 496

IEEE 802.1Q Switch Operation 497 Ingress Process 499

Acceptable Frame Filter 499 Ingress Rules 499 Ingress Filter 500

Progress Process 500 Forwarding in a VLAN-A ware Switch 500

xviii Contents

Maintaining the Filtering Database 501 Egress Process 502

Egress Rules 502 Egress Filter 504

System-Level Switch Constraints 506 GARP VLAN Registration Protocol 506

GVRPUseofGARP 507 Multicast Registration and VLAN Context 508 VLANs and the Spanning Tree ^ 508 The Multiple Spanning Tree Protocol 511

So Exactly What Are They Trying to Accomplish Here? 511 What the Heck Does This All Mean? 512

Tha-tha-tha-tha-tha...That's Right Folks! 512 Multiple Spanning Tree Instance 513 MST Regions 514

Chapter 13 Priority Operation 517 Why Priority? 517 LAN Priority Mechanisms 519

Token Ring Priority Mechanisms 520 FDDI Priority Mechanisms 521 Ethernet Priority Mechanisms 522

VLAN and Priority Tagging 525 Getting into the Priority Business 526 Priority Operation in Switches 529

The Ordering Invariant — Redux 530 IEEE 802.1p 530 Switch Process Flow for Priority Operation 532 Determining Frame Priority on Input 533

Tag, You're It! 533 LAN-Specific User Priority Indication 533 Implicit Priority Determination, or

"Whose Clues Do You Use?" 534 Priority Regeneration 535

Mapping Input Priority to Class-of-Service 536 Class of Service Versus Quality of Service 536 How Many Queues Do You Chueues? 538 Default Priority Mappings 540

Output Scheduling 541 Scheduling Algorithms 541 Indicating the Priority in Transmitted Frames 544 Mapping User Priority to Access Priority

at the Output Port 545 Chapter 14 LAN Security 547

Network Security Overview 548 Hackers, Crackers, Viruses, and Those Confounded Worms 549

Нас and Crac, the Ker Brothers. 549

'

Chapter 15

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

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

Contents xix

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

xx Contents

Chapter 16

Chapter 17

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

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 Make the Switch! Keeping House

Housekeeping Functions Implementation and Performance

(or, It's Tough to Find a Good Housekeeper)

604 605 607

609 610 611 611 613 614 615 615 617 617 618 620 620

621 622 623 624 624 625 625 626 627 627 627 628 628 629 629 630 632 632 632 633 636 637

641 644 645

647

Contents xxi

Switch Data Receive Path Functions 647 Port Interfaces (Receive) 647 Receive Flow Control 649 Link Aggregation Collector 650 Classification Engine 650

Local Sinking of Reserved Multicast Addresses 651 VLAN Ingress Rules 651 Priority Assessment 653 Do It Once and Save the Results 653 Implementation of the Classification Engine 655

VLAN Filters 657 Lookup Engine 658

Generating the Output Vector 659 Maintaining the Filtering Database 662 Lookup Implementation 662

Switch Fabrics 665 Shared Memory 665

Shared Memory Fabric Operation 665 Multicasting in a Shared Memory Architecture 667 Buffer Organization 668 Memory Bandwidth Limitations 671 Increasing the Memory Bandwidth 672

Shared Bus 674 Crosspoint Matrix 677

Multicasting in a Crosspoint Matrix Fabric 677 Crosspoint Matrix Implementation 679 The Head-of-Line Blocking Problem 680 Solving the Head-of-Line Blocking Problem 682 Priority Levels in the Switch Fabric 690

Input Versus Output Queues 690 Input Queues and Shared Memory Switch Fabrics 691 Input Queues, Output Queues, and Flow Control 691

Switch Data Transmit Path Functions 692 Output Filters 692 Output Queues and Priority Handling 695 Link Aggregation Distributor 696 Transmit Flow Control 696 Hey, Kids! What Time Is It? 697 Port Interfaces (Transmit) 697

Appendix: Protocol Parsing 699

References 703

Glossary 711

Index 753