Cloud Native Data Center Networking

Chapter 2. Clos: Network Topology for a New World

Redwoods have an enormous surface area that extends upward into space because they have a propensity to do something called reiteration. A redwood is a fractal. And as they put out limbs, the limbs burst into small trees, copies of the redwood.

Richard Preston

Form is destiny—in networking even more than in life. The structure of the network lays the foundation for everything that follows. Plant a tree and its roots control the flow. Build a torus-like access road and you get a rich, well-knit neighborhood. Design your network as a Clos, and you get this book.

The structure of the new world is the Clos topology (named after one of its inventors, Charles Clos). The cloud native data center infrastructure pioneers wanted to build something that could scale massively. The Clos topology is like a redwood tree, using a somewhat fractal model to scale out. Networking in a Clos topology is pretty much what this book is about. So understanding the Clos topology and its properties is a key requirement for any network engineer or architect.

This chapter is designed to address questions such as:

• What is Clos topology and how is it different from access-agg-core topology?

• What are the characteristics of Clos topology?

• What are the consequences of the Clos topology for data center networking?

• How do you scale a Clos topology?

• What problems turn up in a Clos topology?

We discuss how the Clos topology connects to outside networks ...