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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, please see the PORTING document.) 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/idl.py. 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:

Diagram

         +----------------------------------------+
         |           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:

attached-mac

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.

iface-id

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.

iface-status

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.

vm-id

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}"'