Open vSwitch on Citrix XenServer

This document describes how to build and install Open vSwitch on a Citrix XenServer host. If you want to install Open vSwitch on a generic Linux or BSD host, refer to Open vSwitch on Linux, FreeBSD and NetBSD instead.

Open vSwitch should work with XenServer 5.6.100 and later. However, Open vSwitch requires Python 2.7 or later, so using Open vSwitch with XenServer 6.5 or earlier requires installing Python 2.7.

Building

You may build from an Open vSwitch distribution tarball or from an Open vSwitch Git tree. The recommended build environment to build RPMs for Citrix XenServer is the DDK VM available from Citrix.

  1. If you are building from an Open vSwitch Git tree, then you will need to first create a distribution tarball by running:

    $ ./boot.sh
    $ ./configure
    $ make dist
    

    You cannot run this in the DDK VM, because it lacks tools that are necessary to bootstrap the Open vSwitch distribution. Instead, you must run this on a machine that has the tools listed in Installation Requirements as prerequisites for building from a Git tree.

  2. Copy the distribution tarball into /usr/src/redhat/SOURCES inside the DDK VM.

  3. In the DDK VM, unpack the distribution tarball into a temporary directory and “cd” into the root of the distribution tarball.

  4. To build Open vSwitch userspace, run:

    $ rpmbuild -bb xenserver/openvswitch-xen.spec
    

    This produces three RPMs in /usr/src/redhat/RPMS/i386:

    • openvswitch
    • openvswitch-modules-xen
    • openvswitch-debuginfo

    The above command automatically runs the Open vSwitch unit tests. To disable the unit tests, run:

    $ rpmbuild -bb --without check xenserver/openvswitch-xen.spec
    

Build Parameters

openvswitch-xen.spec needs to know a number of pieces of information about the XenServer kernel. Usually, it can figure these out for itself, but if it does not do it correctly then you can specify them yourself as parameters to the build. Thus, the final rpmbuild step above can be elaborated as:

$ VERSION=<Open vSwitch version>
$ KERNEL_NAME=<Xen Kernel name>
$ KERNEL_VERSION=<Xen Kernel version>
$ KERNEL_FLAVOR=<Xen Kernel flavor(suffix)>
$ rpmbuild \
     -D "openvswitch_version $VERSION" \
     -D "kernel_name $KERNEL_NAME" \
     -D "kernel_version $KERNEL_VERSION" \
     -D "kernel_flavor $KERNEL_FLAVOR" \
     -bb xenserver/openvswitch-xen.spec

where:

<openvswitch version>
is the version number that appears in the name of the Open vSwitch tarball, e.g. 0.90.0.
<Xen Kernel name>
is the name of the XenServer kernel package, e.g. kernel-xen or kernel-NAME-xen, without the kernel- prefix.
<Xen Kernel version>

is the output of:

$ rpm -q --queryformat "%{Version}-%{Release}" <kernel-devel-package>,

e.g. 2.6.32.12-0.7.1.xs5.6.100.323.170596, where <kernel-devel-package> is the name of the -devel package corresponding to <Xen Kernel name>.

<Xen Kernel flavor (suffix)>
is either xen or kdump, where xen flavor is the main running kernel flavor and the kdump flavor is the crashdump kernel flavor. Commonly, one would specify xen here.

For XenServer 6.5 or above, the kernel version naming no longer contains KERNEL_FLAVOR. In fact, only providing the uname -r output is enough. So, the final rpmbuild step changes to:

$ KERNEL_UNAME=<`uname -r` output>
$ rpmbuild \
    -D "kenel_uname $KERNEL_UNAME" \
    -bb xenserver/openvswitch-xen.spec

Installing Open vSwitch for XenServer

To install Open vSwitch on a XenServer host, or to upgrade to a newer version, copy the openvswitch and openvswitch-modules-xen RPMs to that host with scp, then install them with rpm -U, e.g.:

$ scp openvswitch-$VERSION-1.i386.rpm \
    openvswitch-modules-xen-$XEN_KERNEL_VERSION-$VERSION-1.i386.rpm \
    [email protected]<host>:
# Enter <host>'s root password.
$ ssh [email protected]<host>
# Enter <host>'s root password again.
$ rpm -U openvswitch-$VERSION-1.i386.rpm \
    openvswitch-modules-xen-$XEN_KERNEL_VERSION-$VERSION-1.i386.rpm

To uninstall Open vSwitch from a XenServer host, remove the packages:

$ ssh [email protected]<host>
# Enter <host>'s root password again.
$ rpm -e openvswitch openvswitch-modules-xen-$XEN_KERNEL_VERSION

After installing or uninstalling Open vSwitch, the XenServer should be rebooted as soon as possible.

Open vSwitch Boot Sequence on XenServer

When Open vSwitch is installed on XenServer, its startup script /etc/init.d/openvswitch runs early in boot. It does roughly the following:

  • Loads the OVS kernel module, openvswitch.
  • Starts ovsdb-server, the OVS configuration database.
  • XenServer expects there to be no bridges configured at startup, but the OVS configuration database likely still has bridges configured from before reboot. To match XenServer expectations, the startup script deletes all configured bridges from the database.
  • Starts ovs-vswitchd, the OVS switching daemon.

At this point in the boot process, then, there are no Open vSwitch bridges, even though all of the Open vSwitch daemons are running. Later on in boot, /etc/init.d/management-interface (part of XenServer, not Open vSwitch) creates the bridge for the XAPI management interface by invoking /opt/xensource/libexec/interface-reconfigure. Normally this program consults XAPI’s database to obtain information about how to configure the bridge, but XAPI is not running yet(*) so it instead consults /var/xapi/network.dbcache, which is a cached copy of the most recent network configuration.

(*) Even if XAPI were running, if this XenServer node is a pool slave then the
query would have to consult the master, which requires network access, which begs the question of how to configure the management interface.

XAPI starts later on in the boot process. XAPI can then create other bridges on demand using /opt/xensource/libexec/interface-reconfigure. Now that XAPI is running, that program consults XAPI directly instead of reading the cache.

As part of its own startup, XAPI invokes the Open vSwitch XAPI plugin script /etc/xapi.d/openvswitch-cfg-update passing the update command. The plugin script does roughly the following:

  • Calls /opt/xensource/libexec/interface-reconfigure with the rewrite command, to ensure that the network cache is up-to-date.
  • Queries the Open vSwitch manager setting (named vswitch_controller) from the XAPI database for the XenServer pool.
  • If XAPI and OVS are configured for different managers, or if OVS is configured for a manager but XAPI is not, runs ovs-vsctl emer-reset to bring the Open vSwitch configuration to a known state. One effect of emer-reset is to deconfigure any manager from the OVS database.
  • If XAPI is configured for a manager, configures the OVS manager to match with ovs-vsctl set-manager.

Notes

  • The Open vSwitch boot sequence only configures an OVS configuration database manager. There is no way to directly configure an OpenFlow controller on XenServer and, as a consequence of the step above that deletes all of the bridges at boot time, controller configuration only persists until XenServer reboot. The configuration database manager can, however, configure controllers for bridges. See the BUGS section of ovs-testcontroller(8) for more information on this topic.
  • The Open vSwitch startup script automatically adds a firewall rule to allow GRE traffic. This rule is needed for the XenServer feature called “Cross-Host Internal Networks” (CHIN) that uses GRE. If a user configures tunnels other than GRE (ex: Geneve, VXLAN, LISP), they will have to either manually add a iptables firewall rule to allow the tunnel traffic or add it through a startup script (Please refer to the “enable-protocol” command in the ovs-ctl(8) manpage).

Reporting Bugs

Please report problems to bugs@openvswitch.org.