On Wed, Oct 29, 2014 at 02:30:29PM -0400, Aravindhan Dhanasekaran wrote: > On 10/29/2014 01:09 PM, Emma Anderson wrote: > > Hi all, > > > > In openflow manual, existence of openflow entries with identical match > > fields > > but different priorities is allowed. But, what would the point of having > > identical entries in a table, since the second one is never used? > > Even when the match fields are the same, the actions/instructions can be > different. > > Yes, the controller can modify the existing flow entry, but think of an use > case > like this: > * Module X in a controller would have installed a flow with action AA. > * Module Y (has higher priority than module X) would want to install the > same flow with action BB, but for a very short duration. > > If we were to go by replace an existing flow, we need to have interactions > between module X & Y. Instead, we can simply have module Y install a higher > priority flow and have it deleted after a short time. It just makes controller > implementation more easier and modular. > > > I don't think the justification that controller can delete the one with > > higher > > priority at some time would be interesting enough to make the architecture > > more > > complicated, and tables more populated. > > Flow table manipulation is completely left to the controller. OF is just > enabling more options and it's up to the controller to either modify an > existing > flow or to install (and then delete) a higher priority flow. > > These are just my thoughts. Any replies from OF spec design team or controller > dev folks would be more insightful.
When OpenFlow was designed, I don't think we had a particular use case in mind for identical matches with different priorities, but we also didn't know of any good reason to forbid it, so we didn't. In practice, occasionally some clever use like the one described above has come up. That's good enough justification, in my opinion. _______________________________________________ openflow-discuss mailing list openflow-discuss@lists.stanford.edu https://mailman.stanford.edu/mailman/listinfo/openflow-discuss
