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Re: [Coin] Fwd: The Future of P4, Revisited

hemant@mnkcg.com Thu, 18 May 2023 17:10 UTC

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From: hemant@mnkcg.com
To: 'Haoyu Song' <haoyu.song@futurewei.com>, ehalep@mojatatu.com, 'Toerless Eckert' <tte@cs.fau.de>
Cc: hemant=40mnkcg.com@dmarc.ietf.org, "'Bernier, Daniel'" <daniel.bernier@bell.ca>, 'Hesham ElBakoury' <helbakoury@gmail.com>, 'Marie-Jose Montpetit' <marie@mjmontpetit.com>, 'coin' <coin@irtf.org>, coinrg-chairs@ietf.org
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Date: Thu, 18 May 2023 13:10:18 -0400
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Subject: Re: [Coin] Fwd: The Future of P4, Revisited
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Also, the P4 PNA work has sample P4 programs to maintain TCP connection
state.  

Hemant

-----Original Message-----
From: Coin <coin-bounces@irtf.org> On Behalf Of Haoyu Song
Sent: Thursday, May 18, 2023 12:19 PM
To: ehalep@mojatatu.com; 'Toerless Eckert' <tte@cs.fau.de>
Cc: hemant=40mnkcg.com@dmarc.ietf.org; 'Bernier, Daniel'
<daniel.bernier@bell.ca>; 'Hesham ElBakoury' <helbakoury@gmail.com>;
'Marie-Jose Montpetit' <marie@mjmontpetit.com>; 'coin' <coin@irtf.org>;
coinrg-chairs@ietf.org
Subject: Re: [Coin] Fwd: The Future of P4, Revisited

Interesting discussion. See my comments below  [HS]

Haoyu

> For example, in the multicast drafts i write, we use C-pseudocode to 
> specify behavior, but we do attempt to implemnt on Tofino in P4. 
> Should we really use P4 code for the RFC specs... ? (much longer than 
> C Pseudocode). Aka: quite selfish (but IETF relevant ;-) reason to
highlight this point.

[EH]: This is an area I'm very interested in. Having a standardized and
formal language to describe protocols and behavior can bring a lot of
functionality and benefits to the IETF. 
My initial thinking is that having such a blueprint, the IETF could generate
tools to create a reference implementation that can be used for
interoperability purposes therefore decreasing time to test and implement
protocols and therefore RFC publications.

[HS] P4 can only describe dataplane behaviors, so any control plane stuff is
out of scope. For dataplane, if it's used to describe header format, it's
not better than the "struct" in C. The language uses the match-action table
abstraction with an implication of pipeline implementation which may make it
cumbersome or even impossible to describe the  behavior (e.g.,  P4 has very
limited support for stateful processing). In general, I don't think P4 at
its current form can undertake the role for formal protocol specification. 
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