Components of an SDN

A software-defined network infrastructure has two main key components:

• The SDN controller (only one, could be deployed in a highly available cluster)
• The SDN-enabled switches (multiple switches, mostly in a Clos topology in a data center) as shown in the following figure:

An SDN controller is the single brain of the SDN domain. In fact, an SDN domain is very similar to a chassis-based switch. You can imagine the supervisor or management module of a chassis-based switch as an SDN controller and the rest of the line card and I/O cards as SDN switches. The main difference between an SDN network and a chassis-based switch is that you can scale out the SDN with multiple switches, where in a chassis-based switch you are limited to the number of slots in that chassis: