Introduction . . . . . . . . . . . . xvii

How This Book Is Organized . . . . . . . xvii

Chapter 1: Defining Complexity . . . . . . . . . 1

What Is Complexity? . . . . . . . . . 3

Anything I Don’t Understand . . . . . . 3

Anything with a Lot of Parts . . . . . . . 5

Anything for Which There Is More State Than Required to

Achieve a Goal . . . . . . . . . 9

Unintended Consequences . . . . . . 11

Why So Much Complexity? . . . . . . . . 13

Future Extensions versus New Protocols . . . . 16

Unexpected Errors . . . . . . . . 17

Why Not Build Infinitely Complex Systems? . . . . . 18

Quick, Cheap, and High Quality: Choose Two . . . 20

Consistency, Availability, and Partition Tolerance:

Choose Two . . . . . . . . . 21

Journey into the Center of Complexity . . . . . . 22

Chapter 2: Components of Complexity . . . . . . . 25

Network Convergence . . . . . . . . . 26

Path Vector: A BGP Example . . . . . . 26

Distance Vector: An EIGRP Example . . . . . 28

Link State: OSPF and IS-IS Convergence . . . . 30

State . . . . . . . . . . . . 31

Amount of Information . . . . . . . 32

An Example of State Failure in the Real World . . . 33

Final Thoughts on State . . . . . . . 34

Speed . . . . . . . . . . . . 35

The Network That Never Converges . . . . . 35

The Flapping Link . . . . . . . . 37

Final Thoughts on Speed . . . . . . . 38

Surface . . . . . . . . . . . . 38

The Hourglass Model . . . . . . . . . 41

Optimization . . . . . . . . . . . 44

A Final Thought . . . . . . . . . . 46

Chapter 3: Measuring Network Complexity . . . . . . 47

Some Measures of Network Complexity . . . . . 49

Network Complexity Index . . . . . . 49

Modeling Design Complexity . . . . . . 51

NetComplex . . . . . . . . . 53

Organized Complexity . . . . . . . . . 55

Is This a Waste of Time? . . . . . . . . . 58

A Final Thought . . . . . . . . . . 58

Chapter 4: Operational Complexity . . . . . . . . 61

Exploring the Problem Space . . . . . . . . 61

The Cost of Human Interaction with the System . . . 61

Policy Dispersion versus Optimal Traffic Handling . . 66

Solving the Management Complexity Problem . . . . 69

Automation as a Solution to Management Complexity . 69

Modularity as a Solution to Management Complexity . 72

Protocol Complexity versus Management Complexity . 74

A Final Thought . . . . . . . . . . 77

Chapter 5: Design Complexity . . . . . . . . . 79

Control Plane State versus Stretch . . . . . . . 81

Aggregation versus Stretch . . . . . . . 83

Traffic Engineering . . . . . . . . 85

State versus Stretch: Some Final Thoughts . . . . 87

Topology versus Speed of Convergence . . . . . . 88

Ring Topology Convergence . . . . . . 88

Redundancy versus Resilience . . . . . . 90

Topology versus Speed of Convergence:

Some Final Thoughts . . . . . . . 93

Fast Convergence versus Complexity . . . . . . 94

Improving Convergence with Intelligent Timers: Talk Faster . . . . . . . . . 96

Removing Timers from Convergence: Precompute . . 99

Working around Topology: Tunneling to the Loop-Free

Alternate . . . . . . . . . 101

Some Final Thoughts on Fast Convergence . . . 104

Virtualization versus Design Complexity . . . . . 106

Functional Separation . . . . . . . 108

Forwarding Plane Complexity . . . . . . 109

Control Plane Complexity . . . . . . 109

Shared Fate Risk Groups . . . . . . . 111

A Final Thought . . . . . . . . . . 111

Chapter 6: Managing Design Complexity . . . . . . 113

Modularity . . . . . . . . . . . 113

Uniformity . . . . . . . . . 114

Interchangeable Modules . . . . . . . 120

How Modularity Attacks the Complexity Problem . . 121

Information Hiding . . . . . . . . . 122

Aggregation . . . . . . . . . 122

Failure Domains and Information Hiding . . . . 126

Final Thoughts on Information Hiding . . . . 128

Models . . . . . . . . . . . 129

Waterfall . . . . . . . . . . 129

Places in the Network . . . . . . . 131

Hierarchical . . . . . . . . . 132

UML . . . . . . . . . . . 134

A Final Thought . . . . . . . . . . 136

Chapter 7: Protocol Complexity . . . . . . . . 137

Flexibility versus Complexity: OSPF versus IS-IS . . . . 138

Layering versus Protocol Complexity . . . . . . 141

The Seven-Layer Model . . . . . . . 143

The Four-Layer Model . . . . . . . 146

The Iterative Model . . . . . . . . 147

Protocol Stacks and Design . . . . . . 148

Protocol Complexity versus Design Complexity . . . . 149

Microloops and Fast Reroute . . . . . . 149

EIGRP and the Design Conundrum . . . . . 158

Final Thoughts on Protocol Complexity . . . . . 162

Chapter 8: How Complex Systems Fail . . . . . . . 163

Feedback Loops . . . . . . . . . . 164

Positive Feedback Loops in Network Engineering . . 169

Speed, State, and Surface: Stability in the

Network Control Plane . . . . . . . 174

Shared Fate . . . . . . . . . . . 177

Virtual Circuits . . . . . . . . . 177

TCP Synchronization as a Shared Fate Problem . . 179

A Final Thought . . . . . . . . . . 181

Thoughts on Root Cause Analysis . . . . . 181

Engineering Skills and Failure Management . . . 182

Chapter 9: Programmable Networks . . . . . . . 185

Drivers and Definition . . . . . . . . . 186

Business Drivers . . . . . . . . 186

The Ebb and Flow of Centralization . . . . . 188

Defining Network Programmability . . . . . 191

Use Cases for Programmable Networks . . . . . 193

Bandwidth Calendaring . . . . . . . 193

Software-Defined Perimeter . . . . . . 196

Programmable Network Interfaces . . . . . . 200

The Programmable Network Landscape . . . . . 201

OpenFlow . . . . . . . . . . 202

YANG . . . . . . . . . . 204

Path Computation Element Protocol . . . . . 207

Interface to the Routing System . . . . . 210

A Final Thought . . . . . . . . . . 212

Chapter 10: Programmable Network Complexity . . . . . 215

The Subsidiarity Principle . . . . . . . . 216

Policy Management . . . . . . . . . 217

Policy Dispersion . . . . . . . . 220

Policy Consistency . . . . . . . . 222

Policy Complexity . . . . . . . . 223

Surface and the Programmable Network . . . . . 224

Impact on Failure Domains . . . . . . . . 226

Wide Area Failure Domains . . . . . . 227

Data Center Failure Domains . . . . . . 228

Application to Control Plane Failure Domain . . . 229

Controller to Controller Failure Domain . . . . 229

Final Thoughts on Failure Domains . . . . . 229

A Final Thought . . . . . . . . . . 230

Chapter 11: Service Virtualization and Service Chaining . . . . 233

Network Function Virtualization . . . . . . . 234

NFV: A Use Case . . . . . . . . 236

Service Chaining . . . . . . . . . . 242

Service Function Chaining . . . . . . 243

Segment Routing . . . . . . . . 245

A Final Thought . . . . . . . . . . 248

Chapter 12: Virtualization and Complexity . . . . . . 249

Policy Dispersion and Network Virtualization . . . . 250

State and Service Chaining . . . . . . 253

State and Optimization . . . . . . . 254

Surface and Policy Interaction . . . . . . 255

Surface and Policy Proxies . . . . . . 255

Other Design Considerations . . . . . . . 256

Coupling and Failure Domains . . . . . . 257

Troubleshooting . . . . . . . . 260

The Orchestration Effect . . . . . . . . 262

Managing Complexity . . . . . . . . . 264

A Final Thought . . . . . . . . . . 266

Chapter 13: Complexity and the Cloud . . . . . . . 267

Where Does the Complexity Live? . . . . . . 268

Cloud Centric . . . . . . . . . 269

Vendor Centric . . . . . . . . . 270

Network Centric . . . . . . . . 271

Is There a “Right Way?” . . . . . . . 271

Centralize What? . . . . . . . . . . 272

Cloudy Complications . . . . . . . . . 273

Security . . . . . . . . . . 273

Data Portability . . . . . . . . 276

A Final Thought . . . . . . . . . . 277

Chapter 14: A Simple Ending . . . . . . . . . 279

Defining Complexity . . . . . . . . . 279

Difficult to Understand . . . . . . . 280

Unintended Consequences . . . . . . 280

Large Numbers of Interacting Parts . . . . . 280

What Makes Something “Too Complex”? . . . 281

Complexity Is a Tradeoff . . . . . . . . 282

Modeling Complexity . . . . . . . . . 284

Managing Complexity in the Real World . . . . . 286

Don’t Ignore Complexity . . . . . . . 286

Find a Model to Contain the Complexity . . . . 287

A Final Thought . . . . . . . . 288

TOC, 9780133989359, 10/28/2015