[ovs-discuss] mf_value and mf_subvalue size restrictions

Jesse Gross jesse at nicira.com
Thu Nov 6 23:02:45 UTC 2014

On Thu, Nov 6, 2014 at 2:49 PM, Ben Pfaff <blp at nicira.com> wrote:
> On Thu, Nov 06, 2014 at 02:37:01PM -0800, Jesse Gross wrote:
>> I'm curious how you ended up laying this out. The OpenFlow spec says
>> that the extra space should be used as an vendor ID in the form of an
>> OUI. How did you reconcile this?
> You can probably get away with a lot if you make the most significant
> byte of the extra 32 bits nonzero, because OpenFlow only specifies the
> format of the other 24 bits if that byte is zero and leaves the rest of
> the space reserved for future standardization.
> But that's kind of a nasty thing to do.

This crossed my mind as well.

> Have you considered allowing database configuration to specify what kind
> of attributes are expected and how to parse them?  The configuration
> could be P4-based, for example.

This is possible but it seems kind of ugly and complicated so I hope
to not have to go down this path. I think there is a simpler variant,
which is to just have a mapping table of Geneve IDs to a pool of OXMs.
That's all that is really needed since the action to be taken is just
matching against the payload so there isn't much parsing. But I still
would like it avoid this if possible.

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