The Effect of Switch Port Count in Clos Topology
The Clos topology allows you to build very large networks using relatively small building blocks. When the ascent of the hyperscalars began, I’ve heard Google started building networks with 24-port switches, though I can’t be certain as I wasn’t at Google. Around the start of the previous decade, the hyperscalars had moved to using Broadcom’s Trident chip with 64 10GbE ports as the building block. By the end of that decade, Broadcom had started shipping Tomahawk 4 to select customers. Tomahawk 4 is a single packet switching chip that supports 256 ports of 100GbE. Not so long ago, that was an almost mythical number for a single switching ASIC.
The shift to Clos topology as the network topology underlies everything that’s followed in networking in the past decade or more. In this post, we’ll consider the effects of a high switch port count chip such as Tomahawk 4 on the Clos topology. For those interested in more information about Clos topology, please read my book Cloud Native Data Center Networking. A rough summary of that chapter is as follows.
A Terse Introduction to Clos
To most network operators, the Clos topology is the leaf-spine topology, consisting of two layers of switches, one layer called the leaf and the other the spine. The next level up in sophistication is the three-tier Clos…
