..
      Licensed under the Apache License, Version 2.0 (the "License"); you may
      not use this file except in compliance with the License. You may obtain
      a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
      License for the specific language governing permissions and limitations
      under the License.

      Convention for heading levels in Open vSwitch documentation:

      =======  Heading 0 (reserved for the title in a document)
      -------  Heading 1
      ~~~~~~~  Heading 2
      +++++++  Heading 3
      '''''''  Heading 4

      Avoid deeper levels because they do not render well.

===================================
Open vSwitch Without Kernel Support
===================================

Open vSwitch can operate, at a cost in performance, entirely in userspace,
without assistance from a kernel module.  This file explains how to install
Open vSwitch in such a mode.

This version of Open vSwitch should be built manually with ``configure`` and
``make``.  Debian packaging for Open vSwitch is also included, but it has not
been recently tested, and so Debian packages are not a recommended way to use
this version of Open vSwitch.

.. warning::
  The userspace-only mode of Open vSwitch is considered experimental.  It has
  not been thoroughly tested.

Building and Installing
-----------------------

The requirements and procedure for building, installing, and configuring Open
vSwitch are the same as those given in the `installation guide
<INSTALL.rst>`__.  You may omit configuring, building, and installing the
kernel module, and the related requirements.

On Linux, the userspace switch additionally requires the kernel TUN/TAP driver
to be available, either built into the kernel or loaded as a module.  If you
are not sure, check for a directory named ``/sys/class/misc/tun``.  If it does
not exist, then attempt to load the module with ``modprobe tun``.

The tun device must also exist as ``/dev/net/tun``.  If it does not exist, then
create ``/dev/net`` (if necessary) with ``mkdir /dev/net``, then create
``/dev/net/tun`` with ``mknod /dev/net/tun c 10 200``.

On FreeBSD and NetBSD, the userspace switch additionally requires the kernel
tap(4) driver to be available, either built into the kernel or loaded as a
module.

Using the Userspace Datapath with ovs-vswitchd
----------------------------------------------

To use ovs-vswitchd in userspace mode, create a bridge with
``datapath_type=netdev`` in the configuration database.  For example:::

    $ ovs-vsctl add-br br0
    $ ovs-vsctl set bridge br0 datapath_type=netdev
    $ ovs-vsctl add-port br0 eth0
    $ ovs-vsctl add-port br0 eth1
    $ ovs-vsctl add-port br0 eth2

ovs-vswitchd will create a TAP device as the bridge's local interface, named
the same as the bridge, as well as for each configured internal interface.

Currently, on FreeBSD, the functionality required for in-band control support
is not implemented.  To avoid related errors, you can disable the in-band
support with the following command:::

    $ ovs-vsctl set bridge br0 other_config:disable-in-band=true

Firewall Rules
--------------

On Linux, when a physical interface is in use by the userspace datapath,
packets received on the interface still also pass into the kernel TCP/IP stack.
This can cause surprising and incorrect behavior.  You can use "iptables" to
avoid this behavior, by using it to drop received packets.  For example, to
drop packets received on eth0:::

    $ iptables -A INPUT -i eth0 -j DROP
    $ iptables -A FORWARD -i eth0 -j DROP

Other Settings
--------------

On NetBSD, depending on your network topology and applications, the following
configuration might help.  See sysctl(7).::

    $ sysctl -w net.inet.ip.checkinterface=1

Bug Reporting
-------------

Please report problems to bugs@openvswitch.org.