Introduction xxv

Part One Foundations of LAN Switches

Chapter 1 Laying the Foundation 3

Network Architecture 4

Physical Layer 5

Data Link Layer 6

Network Layer 7

Transport Layer 7

Session Layer 8

Presentation Layer 8

Application Layer 9

Layering Makes a Good Servant but a Bad Master 9

Inside the Data Link Layer 12

Modes of Operation 12

Data Link Sublayering 15

Logical Link Control 16

Addressing 19

Local and Global Uniqueness 19

LAN Data Link Addresses 20

Unicast and Multicast Addresses 21

Globally Unique and Locally Unique MAC Addresses 23

How LAN Addresses Are Assigned 24

Written Address Conventions 26

LAN Technology Review 27

Ethernet 27

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

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

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

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

UpaTreeWithoutaProtocol? 252

Why Would Anyone Do This? 252

Interoperability 253

What to Do, What to Do? 253

Chapter 6 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

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

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

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

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-Aware 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-Aware Switch 500

Maintaining the Filtering Database 501

Egress Process 502

Egress Rules 502

Egress Filter 504

System-Level Switch Constraints 506

GARP VLAN Registration Protocol 506

GVRP Use of GARP 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

NetworkSecurityOverview 548

Hackers, Crackers, Viruses, and Those Confounded Worms 549

Hac and Crac, the Ker Brothers. 549

Malware 550

Physical Security 551

Proactive Measures 552

Virus Containment 553

Firewalls 553

End User Checks and Balances 555

LAN Security 555

Security Concerns at Layer 2 555

Man in the Middle 557

MAC Address Table Flooding 557

DHCP Attacks 559

Spanning Tree Attacks 560

Private VLAN Attack 561

VLAN Migration (Hopping) Attack 561

ARP Spoofing Attack 563

Wrap Up 563

Chapter 15 Switch Management 565

The Simple Network Management Protocol 566

SNMP Concepts 568

Manager/Agent Architecture 568

Management Information Base 569

The Simple Network Management Protocol 573

The Simple Network Management Protocol Version 2 575

The Simple Network Management Protocol Version 3 576

Network Monitoring Tools 577

Protocol Analysis in a Switched LAN 580

Mirror, Mirror on the Switch, Which Is the Port That’s Got the Glitch? 581

Switch Mirroring 583

Look Within Yourself for the Truth 585

RMON Capabilities and MIBs 586

Ethernet Statistics Group 586

Ethernet History Group 589

Alarm Group 590

Host Group 591

HostTopN Group 594

Matrix Group 594

Filter Group 596

Packet Capture Group 597

Event Group 597

RMON Support for Virtual LANs 598

Levels of RMON Support 598

Internal Switch Management Platforms 598

Non-SNMP Management 601

Internal Web Servers 602

Out-of-Band Management 602

Management by Telnet 604

Management by Secure Shell 605

Reach Out and Ping Someone 607

Chapter 16 Network Troubleshooting Strategies 609

The Trouble with Troubleshooting 610

Housekeeping 611

Running the Network Baseline 611

Proactive Troubleshooting 613

Troubleshooting Tools 614

Troubleshooting Utilities 615

ping 615

trace route 617

netstat 617

route 618

Arp 620

More Advanced Tools of the Trade 620

Network Analyzers (or whatever they are calling them today) 621

Other Testing Equipment 622

and if all else fails 623

A Systematic Approach 624

Defining the Problem 624

Sharing the Known 625

Determining the Issue 625

Developing a Solution 626

Resolving and Taking Action! 627

Monitoring the Results 627

The Final Step — Have a Beer! 627

Some Strategies for Layer 2 Troubleshooting 628

Performing a Health Check 628

Software, Hardware, and Configuration 629

Issues Relating to Software 629

Issues Relating to Hardware 630

Issues Relating to Configuration 632

Common Layer 2 Issues 632

Vlans 632

Duplex Mismatches 633

Spanning Tree 636

Wrap Up 637

Chapter 17 Make the Switch! 641

Keeping House 644

Housekeeping Functions 645

Implementation and Performance (or, It’s Tough to Find a Good Housekeeper) 647

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