OpenStack, being an open source platform, bundles open source networking solutions as the default implementation for these networking capabilities. For example, routing is supported using namespace, security using iptables, and load balancing using HAproxy.

Historically, these networking capabilities were implemented using customized hardware and software, most of them being proprietary solutions. These custom solutions are capable of much higher performance and are well-supported by their vendors. Hence they have a place in the OpenStack and SDN ecosystem.

From its initial releases, OpenStack has been designed for extensibility. Vendors can write their own extensions and then can easily configure OpenStack to use their extension instead of the default solutions. This allows operators to deploy the networking technology of their choice.

One of the most powerful capabilities of OpenStack is the extensive support for APIs. All OpenStack services interact with one another using well-defined RESTful APIs. This allows custom implementations and pluggable components to provide powerful enhancements for practical cloud implementation.

For example, when a network is created using the OpenStack web interface, a RESTful request is sent to the Horizon service. This in turn, invokes a RESTful API to validate the user using the Keystone service. Once validated, Horizon sends another RESTful API request to Neutron to actually create the network.

In the following chapter, we will see how these RESTful APIs provide support for crucial SDN capabilities in an OpenStack-based cloud.