[P4-dev] filling tables

Sandor Laki lakis at elte.hu
Mon Jul 20 16:55:58 EDT 2015


Hi Salvatore, All,

We faced similar problem when were working on a mac learning example, 
discussed earlier on the dev-list. Unfortunately, the current 
specification does not handle data plane driven table fill and update. 
For example, the mac learning can be done similarly to OpenFlow, using 
two tables (e.g. smac and dmac). As far as I know, the only thing you 
can do is to generate a digest and hand it to a control process running 
on the same switch. Of course, this is not as efficient as a 
data-plane-driven solution, not mentioning aspects like target independence.

Best,
Sandor

2015.07.20. 20:04 keltezéssel, Haoyu song írta:
>
> I agree such active data-path features are very useful and should be 
> considered to add in P4 specification.
>
> Haoyu
>
> *From:*P4-dev [mailto:p4-dev-bounces at p4.org] *On Behalf Of *Salvatore 
> Signorello
> *Sent:* Monday, July 20, 2015 7:05 AM
> *To:* p4-dev at p4.org
> *Subject:* [P4-dev] filling tables
>
> Hi all,
>
> I wonder if there is  a "data-plane"-driven  way to fill/update 
> tables. For example, it could be possible for a match (and so for a 
> packet) to generate a table insertion/update in this way:
>
> table xyz{
>     reads{
>         protocol1.fieldA : exact;
>         protocol2.fieldB : exact;
>     }
>     actions{
>         addEntry; // for example, called the first time the pair 
> {protocol1.fieldA,protocol2.fieldB} has been seen
>         modifyEntry; // from the 2nd packet on, to keep trace of some 
> other information
>    }
> }
>
>
> I would need this to implement a stateful forwarding behavior. Is 
> there any way to express such behavior through the current language 
> specification?
>
> Remark: I don't want to use registers, cause I would rather have an 
> associative facility (key, value) such as a table.
>
> Thank you in advance for any hint,
> best,
> Salvatore
>
>
>
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-- 
Sándor Laki
Department of Information Systems
Eötvös Loránd University
Pázmány Péter stny. 1/C
H-1117, Budapest, Hungary
Room 2.506
Web: http://lakis.web.elte.hu
Phone: +36 1 372 2869 / 8477
Cell: +36 70 374 2646

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