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Software-defined networking in OpenStack with the Neutron module

Neutron Dance

Article from ADMIN 34/2016

By Martin Loschwitz

In classical network settings, software-defined networking (SDN) is a nice add-on, but in clouds, virtual networks are an essential part of the environment. OpenStack integrates SDN technology through the Neutron module.

If you have studied the SDN, you probably know something about cloud computing. SDN would not be as widespread as it is today if cloud solutions such as OpenNebula or OpenStack did not include SDN as an integral component. This article takes a look at Neutron, the OpenStack module that handles SDN management.

SDN Basics

SDN means decoupling management functionality in the network from the switch hardware. Only dumb switches appear in SDN environments: Their task is merely to forward packets from one port to another. They do not split the network into logical segments.

The reason for this simplicity is the need for automation. The configuration of a conventional switch is mostly static; only an admin can change it. But clouds are supposed to work as automatically as possible, and it would be impractical in a cloud to have to change the switch configuration for a new virtual local area network (VLAN) manually once a new customer registers.

Rather than depending on switches, the VLAN function for clouds is provided by the individual computers of the installation. Whatever runs on the computers of the cloud can be configured and automated from the cloud.

The key to SDN is two cloud components: On the one hand, an API interface, typically using the RESTful principle, fields commands from the users, and, on the other hand, agents usually implement the desired configurations on the hosts.

Under the hood, Open vSwitch is almost always used to implement virtual switches on each host. The agents of the cloud solutions thus define a suitable Open vSwitch configuration on the hosts and empower customers to operate virtual networks.

What sounds complicated in theory is easily explained based on the example of OpenStack Neutron. Neutron is the OpenStack SDN component responsible for ensuring that virtual machines (VMs) have a functioning network, that is, a virtual customer

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