Re: [netmod] 6021 ipv4-prefix

"Rob Wilton (rwilton)" <rwilton@cisco.com> Wed, 01 May 2019 16:21 UTC

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From: "Rob Wilton (rwilton)" <rwilton@cisco.com>
To: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>, "Mikael Abrahamsson" <swmike@swm.pp.se>
CC: "netmod@ietf.org" <netmod@ietf.org>
Thread-Topic: [netmod] 6021 ipv4-prefix
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Date: Wed, 1 May 2019 16:21:37 +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: 01 May 2019 16:53
> To: Mikael Abrahamsson <swmike@swm.pp.se>
> Cc: Rob Wilton (rwilton) <rwilton@cisco.com>om>; netmod@ietf.org
> Subject: Re: [netmod] 6021 ipv4-prefix
> 
> On Wed, May 01, 2019 at 03:12:47PM +0200, Mikael Abrahamsson wrote:
> >
> > I am fine with c), but I am also saying I disagree with your view that
> > this this behaviour has been specified "since the beginning". This
> > might have been obvious to you from the beginning, but it's not
> > wrotten down properly (at least I haven't seen text that makes me
> > clearly understand the expected behaviour). I think the text
> > specifying what "canonical format is" referring to "same *value*" is
> > wrong. +17 and 17 is the same integer, 192.168.0.1/24 and
> > 192.168.0.0/24 are not the same *value*. It's misleading to refer to
> > the canonical form having the *same* *value* when we're throwing away
> information.
> >
> 
> The basic disconnect here may be that for me the prefix is the value while for
> you the value is the prefix plus the unused bits.

[To frame this comment, I don't object to your currently proposed solution]

I consider the extra bits after the valid part of the prefix to be unwanted noise.

For me, one hypothetical question I have is whether the potential convenience of allowing 192.168.0.1/24 (for some use cases) outweighs the risk that the wrong value has been provided but cannot be checked (e.g. 192.168.0.1/2).

Similarly, if you consider strings with a max length, I would expect a server to reject a configured string that was too long rather that treat the excessive characters as noise and silently truncate the input.

If it was down to me, and I was defining this now, then I would choose the stricter input (as per the should currently in the ipv6-prefix definition).  But no longer care if the consensus is in the other direction.

Whichever way we change the definitions, I believe that they are being changed in a non-backwards-compatible way that will impact some clients or server implementations.

Thanks,
Rob