..
      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.

================================
OpenFlow Support in Open vSwitch
================================

Open vSwitch support for OpenFlow 1.1 and beyond is a work in progress.  This
file describes the work still to be done.

The Plan
--------

OpenFlow version support is not a build-time option.  A single build of Open
vSwitch must be able to handle all supported versions of OpenFlow.  Ideally,
even at runtime it should be able to support all protocol versions at the same
time on different OpenFlow bridges (and perhaps even on the same bridge).

At the same time, it would be a shame to litter the core of the OVS code with
lots of ugly code concerned with the details of various OpenFlow protocol
versions.

The primary approach to compatibility is to abstract most of the details of the
differences from the core code, by adding a protocol layer that translates
between OF1.x and a slightly higher-level abstract representation.  The core of
this approach is the many ``struct ofputil_*`` structures in
``include/openvswitch/ofp-*.h``.

As a consequence of this approach, OVS cannot use OpenFlow protocol definitions
that closely resemble those in the OpenFlow specification, because
``openflow.h`` in different versions of the OpenFlow specification defines the
same identifier with different values.  Instead, ``openflow-common.h`` contains
definitions that are common to all the specifications and separate protocol
version-specific headers contain protocol-specific definitions renamed so as
not to conflict, e.g. ``OFPAT10_ENQUEUE`` and ``OFPAT11_ENQUEUE`` for the
OpenFlow 1.0 and 1.1 values for ``OFPAT_ENQUEUE``.  Generally, in cases of
conflict, the protocol layer will define a more abstract ``OFPUTIL_*`` or
struct ``ofputil_*``.

Here are the current approaches in a few tricky areas:

* Port numbering.

  OpenFlow 1.0 has 16-bit port numbers and later OpenFlow versions have 32-bit
  port numbers.  For now, OVS support for later protocol versions requires all
  port numbers to fall into the 16-bit range, translating the reserved
  ``OFPP_*`` port numbers.

* Actions.

  OpenFlow 1.0 and later versions have very different ideas of actions.  OVS
  reconciles by translating all the versions' actions (and instructions) to and
  from a common internal representation.

OpenFlow 1.1
------------

OpenFlow 1.1 support is complete.

OpenFlow 1.2
------------

OpenFlow 1.2 support is complete.

OpenFlow 1.3
------------

OpenFlow 1.3 support requires OpenFlow 1.2 as a prerequisite, plus the
following additional work.  (This is based on the change log at the end of the
OF1.3 spec, reusing most of the section titles directly.  I didn't compare the
specs carefully yet.)

* IPv6 extension header handling support.

  Fully implementing this requires kernel support.  This likely will take some
  careful and probably time-consuming design work.  The actual coding, once
  that is all done, is probably 2 or 3 days work.

  (optional for OF1.3+)

* Auxiliary connections.

  An implementation in generic code might be a week's worth of work.  The value
  of an implementation in generic code is questionable, though, since much of
  the benefit of axuiliary connections is supposed to be to take advantage of
  hardware support.  (We could make the kernel module somehow send packets
  across the auxiliary connections directly, for some kind of "hardware"
  support, if we judged it useful enough.)

  (optional for OF1.3+)

* Provider Backbone Bridge tagging.

  I don't plan to implement this (but we'd accept an implementation).

  (optional for OF1.3+)

* On-demand flow counters.

  I think this might be a real optimization in some cases for the software
  switch.

  (optional for OF1.3+)

OpenFlow 1.4 & ONF Extensions for 1.3.X Pack1
---------------------------------------------

The following features are both defined as a set of ONF Extensions for 1.3 and
integrated in 1.4.

When defined as an ONF Extension for 1.3, the feature is using the Experimenter
mechanism with the ONF Experimenter ID.

When defined integrated in 1.4, the feature use the standard OpenFlow
structures (for example defined in openflow-1.4.h).

The two definitions for each feature are independent and can exist in parallel
in OVS.


* Flow entry notifications

  This seems to be modelled after OVS's NXST_FLOW_MONITOR.

  (EXT-187)
  (optional for OF1.4+)

* Flow entry eviction

  OVS has flow eviction functionality.  ``table_mod OFPTC_EVICTION``,
  ``flow_mod 'importance'``, and ``table_desc ofp_table_mod_prop_eviction``
  need to be implemented.

  (EXT-192-e)

  (optional for OF1.4+)

* Vacancy events

  (EXT-192-v)

  (optional for OF1.4+)

* Table synchronisation

  Probably not so useful to the software switch.

  (EXT-232)

  (optional for OF1.4+)

* Group and Meter change notifications

  (EXT-235)

  (optional for OF1.4+)

* PBB UCA header field

  See comment on Provider Backbone Bridge in section about OpenFlow 1.3.

  (EXT-256)

  (optional for OF1.4+)

OpenFlow 1.4 only
-----------------

Those features are those only available in OpenFlow 1.4, other OpenFlow 1.4
features are listed in the previous section.

* Optical port properties

  (EXT-154)

  (optional for OF1.4+)

OpenFlow 1.5 & ONF Extensions for 1.3.X Pack2
---------------------------------------------

The following features are both defined as a set of ONF Extensions for 1.3 and
integrated in 1.5. Note that this list is not definitive as those are not yet
published.

When defined as an ONF Extension for 1.3, the feature is using the Experimenter
mechanism with the ONF Experimenter ID.  When defined integrated in 1.5, the
feature use the standard OpenFlow structures (for example defined in
openflow-1.5.h).

The two definitions for each feature are independent and can exist in parallel
in OVS.

* Time scheduled bundles

  (EXT-340)

  (optional for OF1.5+)

OpenFlow 1.5 only
-----------------

Those features are those only available in OpenFlow 1.5, other OpenFlow 1.5
features are listed in the previous section.

* Egress Tables

  (EXT-306)

  (optional for OF1.5+)

* Flow Entry Statistics Trigger

  (EXT-335)

  (optional for OF1.5+)

* Controller connection status

  Prototype for OVS was done during specification.

  (EXT-454)

  (optional for OF1.5+)

* Port properties for pipeline fields

  Prototype for OVS was done during specification.

  (EXT-388)

  (optional for OF1.5+)

* Port property for recirculation

  Prototype for OVS was done during specification.

  (EXT-399)

  (optional for OF1.5+)

General
-------

* ovs-ofctl(8) often lists as Nicira extensions features that later OpenFlow
  versions support in standard ways.

How to contribute
-----------------

If you plan to contribute code for a feature, please let everyone know on
ovs-dev before you start work.  This will help avoid duplicating work.

Consider the following:

* Testing.

  Please test your code.

* Unit tests.

  Consider writing some.  The tests directory has many examples that you can
  use as a starting point.

* ovs-ofctl.

  If you add a feature that is useful for some ovs-ofctl command then you
  should add support for it there.

* Documentation.

  If you add a user-visible feature, then you should document it in the
  appropriate manpage and mention it in NEWS as well.

Refer to :doc:`/internals/contributing/index` for more information.