OpenFlow version hell

[Prashanth Mundkur <pmundkur.ocaml@xxxxxxxxx>]

As mentioned on today's Mirage call, here are some pointers to
OpenFlow versioning issues.

https://github.com/horms/openvswitch/blob/master/OPENFLOW-1.1%2B#L38

This document underplays the issues, especially for OpenFlow 1.1.
There are major changes in the semantics for flow matching.

- Wildcards vs. exact matching

https://www.opennetworking.org/images/stories/downloads/sdn-resources/onf-specifications/openflow/openflow-spec-v1.0.0.pdf
OF 1.0, Section 3.4:

  Packets are matched against flow entries based on prioritization. An
  entry that specifies an exact match (i.e., it has no wildcards) is
  always the highest priority.  All wildcard entries have a priority
  associated with them. Higher priority entries must match before
  lower priority ones.

https://www.opennetworking.org/images/stories/downloads/sdn-resources/onf-specifications/openflow/openflow-spec-v1.3.1.pdf
OF 1.3.1, Section 5.3:

 The packet is matched against the table and only the highest priority
 flow entry that matches the packet must be selected.

(The language is a little more ambiguous in OF 1.1, but the intent is
 clarified in 1.3.1 above.

 
https://www.opennetworking.org/images/stories/downloads/sdn-resources/onf-specifications/openflow/openflow-spec-v1.1.0.pdf
 Section OF 1.1, Section 4.4:

   The switch should apply the instruction set and update the
   associated counters of only the highest-priority flow entry
   matching the packet.
)

- VLAN tag matching

Summarized here:

https://github.com/horms/openvswitch/blob/master/DESIGN#L155

--prashanth