[P4-dev] What happens during table miss?

Antoine Kaufmann antoinek at cs.washington.edu
Wed Jul 15 22:32:54 EDT 2015

Hi Archie,

what happens with a P4 switch on a table miss is entirely controlled by
the P4 program (plus runtime configuration). If the table has a default
action that was added at runtime from the CPU, then that action will be
executed. Regardless of whether there is a default action, you the
control program can also branch on whether the lookup hit and missed.

If you want the open flow behavior, you can implement this in P4, by
either encapsulating and forwarding the packet to a remote controller,
or locally forwarding it to the CPU.

I hope that helps!


On Wed, Jul 15 18:41, Archie wrote:
> Hi,
>      I know in openflow, when a switch can't find a rule-match for a
> packet, it forwards the packet to the controller. Does the same thing
> happen in P4? Or is a table-miss handled in some other way in P4?
> Thanks,
> Archie

Antoine Kaufmann
<antoinek at cs.washington.edu>
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