How are OVS, OVN, OVSDB and OpenFlow related?

We have seen these OVS, OVN, OVSDB and OpenFlow in various technology articles.  Do you know how they are related?  Or are they related at all?

Well, they all start with the letter "O", this will be great for a Sesame Street episode for us to learn words with the letter "O".  

They all start with the letter O because they are all have "open" in their name.

With "open" in their name, does that make them related?

OVS, OVN, OVSDB and OpenFlow are related but not because they have "open" in their name.

Before we look at how they are related let us take an overview of what they are and some of the key concept that we need to know.  We can only take an overview of OVS, OVN, OVSDB and OpenFlow in this post as they by itself can be one or more blog post to cover.

OVS

OVS is the short form of Open vSwitch.  It is an open source software based virtual network switching module that can be deployed on hypervisor such as KVM or white box switching hardware.   Detail description of OVS can be found on it homepage and GitHub page. 

A list of OVS feature can be found here.  The latest version is release 1.5

OVS is heavily used in OpenStack as KVM is the most deployed hypervsior for OpenStack while OVS is the default virtual switching module for KVM.

This diagram from OVS home page describe what OVS is:

image source: http://openvswitch.org/

As you can see both OpenFlow and OVSDB is related to OVS.  Will discus this in more detail later in this post.

 

OVN

OVN stands for Open Virtual Network and is pronounced as "oven".  This is why the logo looks like the front of an oven.  It is a sub-project within OVS.

Back in March 2015, I have already written an article on OVN.  Please refer to this post for OVN details.

OVSDB

OVSDB is a protocol. It stands for Open vSwtch Database Management protocol. It is used to manage an Open vSwitch. This is the management plan for Open vSwitch. It is defined in RFC 7047.

The heart of OVSDB is the database or schema that defines the configuration of the OVS as well as the QoS policies. Management module uses the JSON-RPC as the transport to communicate with the ovsdb-server module of the OVS. (note: JSON = JavaScript Object Notation and JSON-RPC is a Remote Procedural Call encode in JSON format).

OpenFlow

OpenFlow is a protocol.  It is one form of  control plane for Open vSwitch and is defined in RFC 7149.

The main idea is to setup flow table that defines the action of a particular flow.  The basic action types are forward and drop with other optional/recommended actions such as flood, enqueue or modify field.  

This diagram explains the Flow Table:

 

Putting OVS, OVN, OVSDB and OpenFlow together

This diagram summarize the relationship between OVS, OVSDB and OpenFlow

At this time OVN is part of OVS and uses the same interface ovsdb-server and ovs-vswitchd:

Summary

Both OVS and OVN are open source switching modules with OVSDB as the management plane and OpenFlow is used to program the flow from the controller to the OVS.

Network Virtualization for OVS (Open vSwitch) - Open Virtual Network

Open vSwitch is a open source virtual switch that provide logical switching on hypervisors similar to the VMware vSwitch and the Cisco Nexus 1000V. Full feature of Open vSwitch can be found here.  We can find good resource on Open vSwitch here and here

Open vSwitch has 3 main components:

• ovsdv-vswitchd
• ovsdb-server
• Kernel module

 

image source: http://www.jedelman.com/uploads/9/7/8/6/9786883/8614557.jpg?531

This diagram explain the operation of Open vSwitch very well.  Visually we can see the various components in a physical host (a picture is worth a thousand words).

 

image source: https://networkheresy.files.wordpress.com/2011/06/screen-shot-2011-06-05-at-6-44-32-pm.png

When we look at the features supported by Open vSwitch (OVS), we see that the list is very comprehensive for a switch.  (note: a switch is for layer 2 switching, check out my other post if you are not familiar with the 7 Layers of the OSI model).  There are 2 features on the list that makes OVS a good tool for OpenStack.  The 2 features are:

1. OpenFlow protocol support
2. Multiple tunneling protocols (GRE, VXLAN, IPsec, GRE and VXLAN over IPsec)

According to this article, OVS is the most popular plugin for OpenStack.

Open Virtual Network

On Jan 13, 2015, it was announced that a new sub-project was created under the OVS project - Open Virtual Network (OVN).

The main idea of Open Virtual Network is provide a lightweight control plane that provides native support for common virtual networking abstractions.  

Open Virtual Network (OVN) will include:

• logical switches and routers,
• security groups, and
• L2/L3/L4 ACLs,

and they are to be implemented on top of a an overly network such as VXLAN, NVGRE or GENEVE.   This is  most suitable to integrate with OpenStack Neutron as a plugin.

This article further explain that OVN provide Neutron with improved data plane performance through shortcut, distributed logical L3 processing and in-kernel based security groups, without running special OpenStack agents on hypervisors. Lastly, it will provide a scale-out and highly available gateway solution responsible for bridging from logical into physical space.

OVN will also work with Linux container systems.  Containers are also widely deployed in the OpenStack platforms. I also had a blog post on this topic on my OpenStack for Beginners series.

Open Virtual Network Architecture
Open Virtual Network builds on top of OVS and has the following layers:

1. Open vSwitch
2. OVN Controller
3. OVN Database

Detail of the OVN architecture can be found in this OVN Architectural Guide.

1. Open vSwitch
As Open Virtual Network is a sub-project OVS and is therefore a natural layer for the foundation.  OVS has special extension for OpenFlow support and thus OVN is tailor to how OVS used OpenFlow.  OVN may not work with other OpenFlow implementation.

OVN used the OVS integration guide (IntegrationGuide.md) in the OVS repository.  This defines the interaction between the OVN controller and the hypervisor or container that used the OVS.

2. OVN Controller
This controller resides on each hypervisor and is not a centralized model that is popular on most SDN implementation.  The OVN controller runs on the hypervisor or host as a daemon.  The OVN controller on the southbound interface with the ovs-switchd using the OpenFlow protocol and the ovsdb-server using the OSVDB protocol. And on the northbound interfaces with the OVN Database using the OSVDB protocol.

This diagram is taken from the OVN Architecture Guide:

                             OVN Database
                                    |
                                    |
                          (OVSDB Protocol)
                                    |
   +-------------------------------------------------------------------+
   |                                |                                  |
   |                                |                                  |
   |                           ovn-controller                          |
   |                              |     |                              |
   |                              |     |                              |
   |               +--------------+     +--------------+               |
   |               |                                   |               |
   |               |                                   |               |
   |       (OVSDB Protocol)                       (OpenFlow)           |
   |               |                                   |               |
   |               |                                   |               |
   |         ovsdb-server                         ovs-vswitchd         |
   |                                                                   |
   +---------------------------- Hypervisor ---------------------------+

3. OVN Database
At this initial state of OVN, OVSDB is being used as the OVN Database. One of the design goal for the OVN Database is high availability but the ovsdb-server does not support clustering and it is important to resolve this issue as the OVN is supported to be a production ready feature.

This OVN Database stores 3 types of information:

1. Physical Network Information
2. Logical Network Information
3. Binding (logical element location, logical port and MAC address association)

Cloud Management System
Open Virtual Network requires a Cloud Management System such as OpenStack to function.  There is a plugin available for OpenStack and OVN integration.  This plugin translate the Cloud Management System configuration into the OVN Logical network information (in the form of logical data path flows) that are stored in the OVN Database.

More to come in the near future
Hopefully, we can see more development of this Open Virtual Network soon and if I am able to attend the OpenStack Vancouver summit I will certainly gather more information in this area and share them in this blog.

Reference:

"Features." Features. N.p., n.d. Web. 12 Mar. 2015.

 "OVN, Bringing Native Virtual Networking to OVS." Network Heresy. N.p., 13 Jan. 2015. Web. 12 Mar. 2015.