an extremely brief conceptual introduction to open vswitch

An Extremely Brief Conceptual Introduction to Open vSwitch


Open vSwitch is one of my favorite open source projects.   For those of you who aren’t familiar with it, it’s a switch stack which can by run both as a soft switch (vswitch) within a virtualized environment)and as the control stack for hardware switches. Good stuff.

However, the real kung-fu is that Open vSwitch is built for programmatic state distribution. It does this through two interfaces. One being OpenFlow (with a ton of extensions) for managing the forwarding behaviour of the fast path, and the second being a JSON-RPC based config protocol used for less time critical configuration (tunnels, QoS, NetFlow, etc.). You can view the schema for the config protocol here.


So, what might you do with something like Open vSwitch? Well, the idea is to enable the creation of automated network infrastructure for virtualized environments.

For example, you could use a centralized control system to manage network policies policies that migrate with VMs. This has already been done within the XenServer environment with the Citrix Distributed vSwitch Controller.

Open vSwitch also supports programmatic control of address remapping (L2 and L3 a la OpenFlow), and programmatic control of tunnels as well as multiple tunnel types (e.g. GRE, IPsec, and CAPWAP). These come in handy for various network virtualization functions such as supporting mobility or an L2 service model across subnets.

Open vSwitch is already used in a bunch of production environments. It is most commonly used as a vswitch in large cloud deployments (many thousands of servers) for automated VLAN, policy, and tunnel management. However, I know of a number of deployments which use it as a simple OpenFlow switch, or a more sophisticated programmatic switch to control hardware environments.


Open vSwitch is fast. Damn fast. Some performance tests have shown it to be faster than the native Linux bridge. Open vSwitch uses flow-caching (when running in software), so even under complex configurations the common case should be blazingly fast. Open vSwitch also has highly optimized tunneling implementations.


Open vSwitch is primarily developed and deployed in Linux (however there are ports to other OSes, particularly those used in embedded environments). It is commonly used with both Xen and KVM (there are production environments using both). Further, it has been integrated into a number of cloud management systems including Xen Cloud Platform, OpenQRM, and OpenNebula (a long with a bunch of proprietary CMSes).  It’s currently being integrated into Open Stack.  You can track the progress here.

Why Do I Care?

Mostly because with Open vSwitch, as with other distributed switch solutions, it’s possible to build really sophisticated networks with not-so-sophisticated hardware.  For example, an L3 network from your neighborhood OEM or other other low-cost hardware vendor (check out, for example, Pronto), plus Open vSwitch and a bit of programming can equate to a cheap, bad-ass network for virtual deployments.  But that, my friends, is a topic for another post.

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