OpenStack Quantum is a cloud networking controller and a networking-as-a-service project within the OpenStack cloud computing initiative. Quantum includes a set of application program interfaces (APIs), plug-ins and authentication/authorization control software that enable interoperability and orchestration of network devices and technologies within infrastructure-as-a-service (IaaS) environments.
Quantum was introduced as a core part of OpenStack with the initiative's Folsom release. Prior to the Folsom release, networking functionality was hard-coded in the Nova compute module of OpenStack, which required developers to modify both compute and network features of OpenStack together. With Quantum, networking is a more modular element of OpenStack that can evolve independently.
The core Quantum API includes support for Layer 2 networking and IP address management (IPAM), as well as an extension for a Layer 3 router construct that enables routing between Layer 2 networks and gateways to external networks. Quantum includes a growing list of plugins that enable interoperability with various commercial and open source network technologies, including routers, switches, virtual switches and software-defined networking (SDN) controllers.