A virtual switch is defined as a software application or service that connects virtual machines to virtual networks at the data link layer of the OSI model, also known as layer 2. Neutron supports multiple virtual switching platforms, including Linux bridges provided by the bridge kernel module and Open vSwitch. Open vSwitch, also known as OVS, is an open source virtual switch that supports standard management interfaces and protocols, including NetFlow, SPAN, RSPAN, LACP, and 802.1q VLAN tagging. However, many of these features are not exposed to the user through the OpenStack API. In addition to VLAN tagging, users can build overlay networks in software using L2-in-L3 tunneling protocols, such as GRE or VXLAN. Virtual switches can be used to facilitate communication between instances and devices outside the control of OpenStack, which include hardware switches, network firewalls, storage devices, bare-metal servers, and more.

Additional information on the use of Linux bridges and Open vSwitch as switching platforms for OpenStack can be found in Chapter 4, Virtual Network Infrastructure Using Linux Bridges, and Chapter 5, Building a Virtual Switching Infrastructure Using Open vSwitch, respectively.