Remembering The Management Plane
Posted: September 15, 2012
[This post was written with input from Martin Casado, Ben Pfaff, Justin Pettit and Ben Basler.]
The Open vSwitch (OVS) project is obviously dear to our hearts at Nicira (and now VMware). OVS is a fairly standard open source project, with many dozens of people from companies around the world contributing patches and reviewing them. However, there is more to openness than just open source software; open protocols (with freely accessible specs) are also important. Of course, Open vSwitch is well known as an implementation of the OpenFlow protocol, for which the specs are freely available. But there is another protocol, arguably just as important as OpenFlow, which is used to manage Open vSwitch instances. That protocol is known as the Open vSwitch Data Base management protocol or OVSDB protocol. While the specification of that protocol can be found within the Open vSwitch sources, it’s a bit of an effort to figure out exactly how it works. With that in mind, as well as a desire to be as open as possible, we decided to publish a spec for the OVSDB protocol in a more familiar and accessible format – an Internet draft.
To be clear, anyone can publish an Internet draft, and that does not make something into a standard. There’s a possibility that this Internet draft may be suitable for publication as an informational RFC. That wouldn’t make it a standard either, but it would at least provide an archival publication mechanism for a protocol that is quite widely used. Whether that happens or not depends on the “Independent Stream Editor”, part of the rather complex organization that handles RFC publication. (See http://www.rfc-editor.org/RFCeditor.html.)
So, what is this OVSDB protocol? Obviously, you could just go and read our new Internet draft, but here is the quick summary. While OpenFlow establishes flow state in a switch, there’s a lot more to Open vSwitch – indeed there is more to networking – than just setting up flow (or forwarding) table entries. In Open vSwitch, you can create many virtual switch instances, attach interfaces to those switches, set QOS policies on interfaces, and so on. None of these configuration tasks can be done with OpenFlow, so you need a management/configuration protocol to do them.
The OVSDB protocol has been part of the Open vSwitch implementation for many years. It is essentially a general purpose protocol for interacting with a database, and in Open vSwitch the database in question is a set of tables representing switch configuration data. (Some readers may be familiar with of-config – the OpenFlow config protocol – a more recent effort; we believe that protocol could actually be implemented on top of OVSDB.)
To step back for a moment, networking folks often think of any network device as having a control plane and a data plane. Sadly, the management plane has been all too often neglected. OVSDB is a protocol that was created to address that important but neglected aspect of networking. We think that making networks dramatically easier to manage is in fact one of the major benefits of network virtualization. That’s a topic we’ve discussed elsewhere; for now, I’ll just urge readers of this blog to go take a look at our current approach to managing and configuring Open vSwitch instances.