Re: [netmod] 6021 ipv4-prefix

"Rob Wilton (rwilton)" <rwilton@cisco.com> Mon, 29 April 2019 13:33 UTC

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From: "Rob Wilton (rwilton)" <rwilton@cisco.com>
To: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
CC: "Acee Lindem (acee)" <acee@cisco.com>, "netmod@ietf.org" <netmod@ietf.org>
Thread-Topic: [netmod] 6021 ipv4-prefix
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Date: Mon, 29 Apr 2019 13:33:22 +0000
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Subject: Re: [netmod] 6021 ipv4-prefix
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> -----Original Message-----
> From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
> Sent: 29 April 2019 11:35
> To: Rob Wilton (rwilton) <rwilton@cisco.com>
> Cc: Acee Lindem (acee) <acee@cisco.com>om>; netmod@ietf.org
> Subject: Re: [netmod] 6021 ipv4-prefix
> 
> On Mon, Apr 29, 2019 at 10:19:01AM +0000, Rob Wilton (rwilton) wrote:
> >
> > It is obvious to me that internally the router should treat these the same, i.e. in
> the canonical format.
> > It is also obvious to me that the operational value reported for this should be
> "10.0.0.0/8".
> >
> > But it isn't obvious to me that if the input configuration contains "10.0.0.1/8"
> then when the client requests that configuration back again it should get
> "10.0.0.0/8" back rather than the value that they provided in the input
> configuration.
> >
> > To me, that probably means that a sensible client should just use the canonical
> format.  Does it improve interop for the type to allow the non-canonical format
> on input?  That isn't obvious to me either.
> >
> 
> We have the same with +7 and 7 - if you configure an integer to be +7 you get
> the value 7 back. The alternative would be to generally disallow any types that
> accept multiple representations in YANG. This would then be a YANG next issue
> to bring up. In YANG 1 and 1.1, we do support "liberal inputs". (And yes, I know
> that some of this is also encoding specific, the hidden can or worms is indeed
> bigger. But I like to have this discussion scoped to the RFC 6991bis effort.)

I think that there is a difference between a canonical representation for base types known to YANG, vs a defined canonical representation in a typedef's description that requires additional typedef specific code to behave correctly under various scenarios (e.g. server input, when comparing instance values).

I do agree that a clarification is better than the ambiguity that we have now.

But I'm not convinced that allowing ipv4-prefix values in the non-canonical format is necessarily the right thing to do.  If we were defining these as a new type today then would we make the same choice of typedef definition?

Or is a significant part of your proposal/reasoning to ensure backwards compatibility with what we have today?

Thanks,
Rob


> 
> /js
> 
> --
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>