Integration Guide for Centralized Control

This document describes how to integrate Open vSwitch onto a new platform to expose the state of the switch and attached devices for centralized control. (If you are looking to port the switching components of Open vSwitch to a new platform, refer to Porting Open vSwitch to New Software or Hardware) The focus of this guide is on hypervisors, but many of the interfaces are useful for hardware switches, as well. The XenServer integration is the most mature implementation, so most of the examples are drawn from it.

The externally visible interface to this integration is platform-agnostic. We encourage anyone who integrates Open vSwitch to use the same interface, because keeping a uniform interface means that controllers require less customization for individual platforms (and perhaps no customization at all).

Integration centers around the Open vSwitch database and mostly involves the external_ids columns in several of the tables. These columns are not interpreted by Open vSwitch itself. Instead, they provide information to a controller that permits it to associate a database record with a more meaningful entity. In contrast, the other_config column is used to configure behavior of the switch. The main job of the integrator, then, is to ensure that these values are correctly populated and maintained.

An integrator sets the columns in the database by talking to the ovsdb-server daemon. A few of the columns can be set during startup by calling the ovs-ctl tool from inside the startup scripts. The xenserver/etc_init.d_openvswitch script provides examples of its use, and the ovs-ctl(8) manpage contains complete documentation. At runtime, ovs-vsctl can be be used to set columns in the database. The script xenserver/etc_xensource_scripts_vif contains examples of its use, and ovs-vsctl(8) manpage contains complete documentation.

Python and C bindings to the database are provided if deeper integration with a program are needed. The XenServer ovs-xapi-sync daemon (xenserver/usr_share_openvswitch_scripts_ovs-xapi-sync) provides an example of using the Python bindings. More information on the python bindings is available at python/ovs/db/ Information on the C bindings is available at lib/ovsdb-idl.h.

The following diagram shows how integration scripts fit into the Open vSwitch architecture:


         |           Controller Cluster           +
|                            |                             |
|             +--------------+---------------+             |
|             |                              |             |
|   +-------------------+           +------------------+   |
|   |   ovsdb-server    |-----------|   ovs-vswitchd   |   |
|   +-------------------+           +------------------+   |
|             |                              |             |
|  +---------------------+                   |             |
|  | Integration scripts |                   |             |
|  | (ex: ovs-xapi-sync) |                   |             |
|  +---------------------+                   |             |
|                                            |   Userspace |
|                                            |      Kernel |
|                                            |             |
|                                 +---------------------+  |
|                                 |  OVS Kernel Module  |  |
|                                 +---------------------+  |

A description of the most relevant fields for integration follows. By setting these values, controllers are able to understand the network and manage it more dynamically and precisely. For more details about the database and each individual column, please refer to the ovs-vswitchd.conf.db(5) manpage.

Open_vSwitch table

The Open_vSwitch table describes the switch as a whole. The system_type and system_version columns identify the platform to the controller. The external_ids:system-id key uniquely identifies the physical host. In XenServer, the system-id will likely be the same as the UUID returned by xe host-list. This key allows controllers to distinguish between multiple hypervisors.

Most of this configuration can be done with the ovs-ctl command at startup. For example:

$ ovs-ctl --system-type="XenServer" --system-version="6.0.0-50762p" \
    --system-id="${UUID}" "${other_options}" start

Alternatively, the ovs-vsctl command may be used to set a particular value at runtime. For example:

$ ovs-vsctl set open_vswitch . external-ids:system-id='"${UUID}"'

The other_config:enable-statistics key may be set to true to have OVS populate the database with statistics (e.g., number of CPUs, memory, system load) for the controller’s use.

Bridge table

The Bridge table describes individual bridges within an Open vSwitch instance. The external-ids:bridge-id key uniquely identifies a particular bridge. In XenServer, this will likely be the same as the UUID returned by xe network-list for that particular bridge.

For example, to set the identifier for bridge “br0”, the following command can be used:

$ ovs-vsctl set Bridge br0 external-ids:bridge-id='"${UUID}"'

The MAC address of the bridge may be manually configured by setting it with the other_config:hwaddr key. For example:

$ ovs-vsctl set Bridge br0 other_config:hwaddr="12:34:56:78:90:ab"

Interface table

The Interface table describes an interface under the control of Open vSwitch. The external_ids column contains keys that are used to provide additional information about the interface:


This field contains the MAC address of the device attached to the interface. On a hypervisor, this is the MAC address of the interface as seen inside a VM. It does not necessarily correlate to the host-side MAC address. For example, on XenServer, the MAC address on a VIF in the hypervisor is always FE:FF:FF:FF:FF:FF, but inside the VM a normal MAC address is seen.


This field uniquely identifies the interface. In hypervisors, this allows the controller to follow VM network interfaces as VMs migrate. A well-chosen identifier should also allow an administrator or a controller to associate the interface with the corresponding object in the VM management system. For example, the Open vSwitch integration with XenServer by default uses the XenServer assigned UUID for a VIF record as the iface-id.


In a hypervisor, there are situations where there are multiple interface choices for a single virtual ethernet interface inside a VM. Valid values are “active” and “inactive”. A complete description is available in the ovs-vswitchd.conf.db(5) manpage.


This field uniquely identifies the VM to which this interface belongs. A single VM may have multiple interfaces attached to it.

As in the previous tables, the ovs-vsctl command may be used to configure the values. For example, to set the iface-id on eth0, the following command can be used:

$ ovs-vsctl set Interface eth0 external-ids:iface-id='"${UUID}"'

HA for OVN DB servers using pacemaker

The ovsdb servers can work in either active or backup mode. In backup mode, db server will be connected to an active server and replicate the active servers contents. At all times, the data can be transacted only from the active server. When the active server dies for some reason, entire OVN operations will be stalled.

Pacemaker is a cluster resource manager which can manage a defined set of resource across a set of clustered nodes. Pacemaker manages the resource with the help of the resource agents. One among the resource agent is OCF

OCF is nothing but a shell script which accepts a set of actions and returns an appropriate status code.

With the help of the OCF resource agent ovn/utilities/ovndb-servers.ocf, one can defined a resource for the pacemaker such that pacemaker will always maintain one running active server at any time.

After creating a pacemaker cluster, use the following commands to create one active and multiple backup servers for OVN databases:

$ pcs resource create ovndb_servers ocf:ovn:ovndb-servers \
     master_ip=x.x.x.x \
     ovn_ctl=<path of the ovn-ctl script> \
     op monitor interval="10s" \
     op monitor role=Master interval="15s"
$ pcs resource master ovndb_servers-master ovndb_servers \
    meta notify="true"

The master_ip and ovn_ctl are the parameters that will be used by the OCF script. ovn_ctl is optional, if not given, it assumes a default value of /usr/share/openvswitch/scripts/ovn-ctl. master_ip is the IP address on which the active database server is expected to be listening.

Whenever the active server dies, pacemaker is responsible to promote one of the backup servers to be active. Both ovn-controller and ovn-northd needs the ip-address at which the active server is listening. With pacemaker changing the node at which the active server is run, it is not efficient to instruct all the ovn-controllers and the ovn-northd to listen to the latest active server’s ip-address.

This problem can be solved by using a native ocf resource agent ocf:heartbeat:IPaddr2. The IPAddr2 resource agent is just a resource with an ip-address. When we colocate this resource with the active server, pacemaker will enable the active server to be connected with a single ip-address all the time. This is the ip-address that needs to be given as the parameter while creating the ovndb_servers resource.

Use the following command to create the IPAddr2 resource and colocate it with the active server:

$ pcs resource create VirtualIP ocf:heartbeat:IPaddr2 ip=x.x.x.x \
    op monitor interval=30s
$ pcs constraint order promote ovndb_servers-master then VirtualIP
$ pcs constraint colocation add VirtualIP with master ovndb_servers-master \