[P4-design] A thought on "reject" in the parser

David George david.george at netronome.com
Fri Aug 4 08:54:22 EDT 2017

The spec says:

>> An architecture must specify the behavior when the accept and reject
states are reached. For example,
>> an architecture may specify that all packets reaching the reject state
are dropped without further pro-
>> cessing. Alternatively, it may specify that such packets are passed to
the next block after the parser, with
>> intrinsic metadata indicating that the parser reached the reject state,
along with the error recorded.

I'm wondering how the architecture would specify this. I would assume in a
document and not in the model P4 source. Is this correct?

My feeling is that this behaviour is a little vague. I was thinking it
might be better to allow the user to define a custom "reject" parse node
which explicitly performs this function. If the reject node is not defined
then the packet is rejected.

This would make it possible to implement something like parser exceptions
in P4-16.

David George
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