Controller-Based LAN Fundamentals

Jeff Smith, Jake Woodhams, Robert Marg

Cisco Press 800 East 96th Street

Indianapolis, IN 46240

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Contents Introduction xvi

Chapter 1 The Need for Controller-Based Wireless Networks 1

Why Wireless LAN Controllers Were Created 4

Why You Need to Use a Wireless LAN Controller 5

Controller-Based WLAN Functional and Elemental Architecture 6

Autonomous AP Issues and the WLC Remedy 9

Problem: WLAN APs Are Difficult to Deploy 9

Problem: WLANs Are Not Secure 10

Problem: Infrastructure Device Configuration and Scaling 10

Problem: Autonomous AP Costs for Configuring Each AP 11

Problem: Autonomous AP Costs for Keeping Each AP's Software Up to Date 11

Problem: RF Expertise and Configuration Challenges 12

Mobility Applications Enabled by Controller-Based WLANs 12

WLANs Do Not Provide the Performance and Robustness Needed

for Use as a Primary Access Network 13

Summary 13

Chapter 2 Wireless LAN Protocols 15

Understanding the Relevant Standards 15

Wi-Fi Alliance 16

Cisco Compatible Extensions 18

IETF 18

The Physical Layer 19

Physical Layer Concepts 19

CAPWAP 21

CAPWAP Versus LWAPP 22

CAPWAP Protocol Fundamentals 23

CAPWAP Terminology 23

CAPWAP Control Messages 24

CAPWAP Data Messages 24

CAPWAP State Machine 24

CUWN Implementation of the CAPWAP Discovery 26

CAPWAP Transport 28

CAPWAP MAC Modes 29

Split MAC Mode 29

Local MAC Mode 30

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Summary of CAPWAP 31 Packet Flow in the Cisco Unified Wireless Network 32

CAPWAP Control 32 CAPWAP Data Path: Centrally Bridged Traffic 32 CAPWAP Data Path: Locally Bridged Traffic 33 Summary of Packet Flow 34

Summary 34 References 34

Chapter 3 802.11n 37

IEEE 802.1 In Standard 38 802.1 In MAC 39 Other 802.11 Standards Used with 802.11n 41 Frequency Bands Supported by 802.1 In 42

Antenna Arrays 42 Transmit Beam Forming (TxBF) 43 Beam Steering 44 Spatial Multiplexing 45 Transmit Diversity 47

Multiple Input, Multiple Output (MIMO) 48 Multipath 48 MIMO Nomenclature 49 Receiver Diversity 51 Branch Selection Diversity 52

Branch-Combining Diversity 53

Diversity Antenna Array, Type, Orientation, and Spacing 55

Transmit Beam-Forming Types 56

Legacy Beam Forming 57

Implicit Beam Forming 57

Explicit Beam Forming 57

MIMO Antenna Array Coverage and Placement 58 Coding 58

Binary Convolutional Coding (BCC) 59 Low-Density Parity Checking (LDPC) 59

HT PHY and Operation 60 HT Mixed 61 HT-Greenfield Format 61

Channel Bonding/40-MHz-Wide Channels 63 Protection 64

Power Management 66

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Packet Aggregation 67 Bursting/Block ACK (BACK) 69 Short Guard Interval (Gl) 69 Reduced Inter-Frame Spacing (RIFS) 69

Reverse Direction Protocol (RDP) 71 Modulation and Coding Schemes (MCS) 71 Configuration Requirements to Obtain HT Rates 73 Predicting 802.11 Link Performance 76 Summary 77

Chapter 4 Cisco Unified Wireless LAN Security Fundamentals 79

Understanding WLAN Security Challenges 80 Vulnerabilities Inherent to the Radio Transmission Medium 80 Physical Containment Problem 81

Unlicensed Radio Spectrum Problem 81

Vulnerabilities Inherent to the Standards Definitions 82

Authentication and Encryption Weaknesses 82

Unauthenticated Management Frames 83

Vulnerabilities Inherent to Mobility 84 Misconfigured Wireless Devices and Clients 85 Rogue Access Points and Devices 85 Readily Available Profiling and Attack Tools 86

Addressing the WLAN Security Challenges 86 Background on Strong Authentication and Privacy 87

How WEP Encryption Works 87

How WEP Is Broken 90

802.11 Authentication 90

Addressing the Strong Authentication and Privacy Challenges 92

Authentication Framework 94

Authentication Algorithm 96

Data Privacy and Integrity 102

Alternative Approaches to Authentication and Data Privacy 113 Rogue Access Point Detection and Wireless Intrusion Prevention 114 Secure Management and Security Policies 118

Summary 119 References 119

Chapter 5 Design Considerations 123

100 Percent Wireless Access Layer 123 Client Device Power 124 RF Vulnerability 124 Volume of Network Traffic 125

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Increased and Difficult WLAN Coverage Requirements 125 Elevators 126

External Bleed-Through 126

Elevator Shaft Coverage 127

Access Point Installed in Elevator Car 127

Continuous Availability and Outage Planning 128

Power Loss 129

Equipment Failures: APs, WLCs, and Backhaul Network 129

RF Interference 131

Denial of Service Attacks 131

Business Operation Continuity in the WLAN Era 132

Power Conservation 132 Flexibility 133 WLAN Capacity 133 Summary 134

Chapter 6 Cisco Unified Wireless LAN Architectures 135 Cisco Unified Wireless LAN Architecture Review 135 Architectural Flexibility, Scalability, and Resiliency 137

Architectural Flexibility 137 Architectural Resiliency 139 N.1WLC Redundancy 141

N:N WLC Redundancy 141

N:N:1WLC Redundancy 142

Architectural Scalability 143

Mobility 143

Mobility Domains 147

Campus Architectures 149 Enterprise Wiring Closet Deployment 149 Enterprise Distribution Layer Deployment 150 Data Center or Services Block Deployments 151 Campus HREAP 152

Branch Architectures 153 Distributed Branch Controller Placement 153 Centralized Controller Placement with HREAP 154 Office Extend AP (OEAP) 155

Summary 155

Chapter 7 Troubleshooting 157 Tools for Troubleshooting 802.11 Wireless Networks 158

Wireless LAN Controller Command-Line Interface 159 Wireless Control System (WCS) 160 Wireless Protocol Analyzer 160 Spectrum Analyzers 162

Isolating Issues on the Cisco Unified Wireless Network 163 Protocol/Network Issues 164 LWAPP/CAPWAP Discovery Process 165 Troubleshooting the LWAPP CAPWAP Discovery Process 167 Network Considerations 170 Client Troubleshooting 170 Troubleshooting Client Issues Using the WLC СЫ 171 Troubleshooting Client Issues Using WCS 172 Common Client Problems and Solutions 176

The Wireless Medium: Troubleshooting Performance-Related Issues 180 Coverage and Interference Issues 180 Detecting, Isolating, and Solving Coverage Issues 181 Detecting, Isolating, and Solving Interference Issues 183

Troubleshooting Advanced Wireless LAN Services 186 Voice over WLAN 186 Voice over WLAN Challenges 187 Troubleshooting VoWLAN 188 Location Troubleshooting 191 Troubleshooting Location Accuracy 192

Summary 194 Chapter 8 Introduction to WCS 195

Designing Wireless Networks with WCS 196 WCS Requirements 197 WCS Interface 197 WCS Monitoring 199 Maps 199 Controllers and AP Monitor 204 Client Monitoring 206 WCS Reporting 209 WCS Configuration 210 Controller Configuration Templates 212 WCS Configuration and Template Auditing 216 AP Configuration Templates 220

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WCS Services 223 WCS Administration 224

Role-Based Access Control (RBAC) 225

WCS Virtual Domains 228

WCS License Center 235

Additional Benefits of WCS: Planning and Calibration Tools 236 WCS Planning 236 WCS Calibration 238

Summary 241

Chapter 9 Next-Generation Advanced Topics: Multicast 243

Multicast 244 Multicast Definition 245 Multicast Addressing 246

Multicast Forwarding 249

Multicast Distribution Trees 249

Protocol Independent Multicasting (PIM) 250

IGMP 253

Multicast Configuration in the CUWN 256 Access Point-to-Client Delivery 256 Client-to-Access Point Delivery 256 Enabling Multicast on a Cisco WLAN Controller 259 MGIDs 262 Multicast Mobility Messaging 264 Enabling Multicast on a Cisco Router or Layer 3 Switch 265

VideoStream 267 Principles of VideoStream 268 Multicast Reliability 268

QoS 269

Configuring VideoStream on the WLC 272 Additional Design Recommendations 275

Wireless Multicast Roaming 275 Wireless CAPWAP Fragmentation 277 All WLCs Have the Same CAPWAP Multicast Group Address 278 WLC Placement 279

Summary 280

Index 281