Re: [netmod] 6021 ipv4-prefix

Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> Mon, 29 April 2019 09:47 UTC

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Date: Mon, 29 Apr 2019 11:47:31 +0200
From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
To: Martin Bjorklund <mbj@tail-f.com>
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Subject: Re: [netmod] 6021 ipv4-prefix
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On Mon, Apr 29, 2019 at 10:48:25AM +0200, Martin Bjorklund wrote:
> 
> I did some digging, and it turns out that we had this type internally
> before it was part if ietf-inet-types, where we did not require that
> all non-prefix bits were zero, but at one point (after
> draft-ietf-netmod-yang-types-00 back in 2008) checked in a fix:
> 
>   The confd:ipv4Prefix and confd:ipv6Prefix types now require that all
>   bits that do not belong to the prefix are set to zero. This is for
>   compatibility with the corresponding YANG types defined by the IETF
>   NETMOD working group.
> 
> You may want to see the threads:
> 
> https://mailarchive.ietf.org/arch/msg/netmod/bXL0Mec_ZVVyalmK3pNHkczm6ZI
> 
> https://mailarchive.ietf.org/arch/msg/netmod/3Wz5BPgxZajCZloAOjU-ycfr9Lg
> 
> Specifically Juergen's proposal:
> 
>       Require that all bits that are not part of the prefix are set to
>       zero (192.0.2.8/24 becomes an invalid representation of an IPv4
>       prefix)
> 
> I can't find any discussion in the archive about allowing non-zero non-prefix
> bits.  So I think that the original intention was to be strict in
> these types.  I agree that the current description text needs
> clarification in either case.

Looking at the archive again, the second message seems to indicate
that the idea was to require non-prefix bits to be zero for IPv4 but
not for IPv6, which could explain why we have the SHOULD text for
ip6-prefix but not for ipv4-prefix. In retrospect, having different
requirements for non-prefix bits in ipv4-prefix and ip6-prefix sounds
somewhat weird. The first message you refer to only indicates that we
need to think about canonical formats for the ipvX-prefix types.

Since the text does not say that non-zero non-prefix bits are
disallowed, I think the clarification I have proposed is a path
forward to resolve this.

/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/>