[ovs-dev] [PATCH 15/17] nx-match: Add support for experimenter OXM.

[YAMAMOTO Takashi]

> On Wed, Sep 24, 2014 at 10:57:08AM +0900, YAMAMOTO Takashi wrote:
>> > Testing experimenter OXM is tricky because I do not know of any in
>> > widespread use.  Two ONF proposals use experimenter OXMs: EXT-256 and
>> > EXT-233.  EXT-256 is not suitable to implement for testing because its use
>> > of experimenter OXM is wrong and will be changed.  EXT-233 is not suitable
>> 
>> sorry for sidetracking, how EXT-256 is wrong and will be changed?
>> i'm interested because i implemented the extension in Ryu.
> 
> The original design for OXM had 32-bit standard OXMs and 64-bit
> experimenter OXMs.  Then, later on, somehow this design was forgotten,
> and experimenter OXMs were re-envisioned as 72, 80, 88, or 96 bits
> long, where the additional 8 to 32 bits provided additional
> experimenter-defined field information.  This is difficult to handle
> because the length of the additional bits is experimenter-specific, so
> that a switch or controller cannot figure out whether two fields are
> even the same unless it knows how long the additional bits are for
> some specific experimenter.  It is also not explained in the standard
> anywhere.  I don't know where it came from, but it seems like a
> mistake and will be rectified by reissuing a corrected EXT-256.  It
> should not be necessary to actually change the OpenFlow standard
> otherwise, since the standard didn't actually say to do anything this
> way.

thank you for explanation.
i remember that it was a mystery what oxm_field should be for EXT-256.

YAMAMOTO Takashi