Re: Objection to draft-ietf-6man-rfc4291bis-07.txt

David Farmer <farmer@umn.edu> Sat, 25 February 2017 20:40 UTC

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From: David Farmer <farmer@umn.edu>
Date: Sat, 25 Feb 2017 14:40:40 -0600
Message-ID: <CAN-Dau0fq9eU71Od3oq9DRq1qLLMqiW-gr-oxgkc46Xo6hjE+Q@mail.gmail.com>
Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Cc: Alexandre Petrescu <alexandre.petrescu@gmail.com>, 6man WG <ipv6@ietf.org>
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On Sat, Feb 25, 2017 at 1:15 PM, Brian E Carpenter <
brian.e.carpenter@gmail.com>; wrote:

> On 25/02/2017 23:02, Alexandre Petrescu wrote:
> ...
> > I would agree if I read "/64 was RECOMMENDED in the past".
>
> That would be a lie, since until now it was 'required' in the text.
>
> > I would not agree if I read "/64 is NOT RECOMMENDED".
>
> But nobody is suggesting that (in RFC 2119 it is equal to SHOULD NOT).
>
> > I would not agree if I read "/64 is RECOMMENDED".
>
> There I think you are wrong. It is the value that today allows portable
> interoperable host software (on IEEE 802.1 or 802.11 media) so it is, in
> fact, the only plausible default that we can suggest. 'Recommended' leaves
> plenty of space that 'required' does not.
>
>     Brian
>

So we can't simply say "/64 subnet prefixes are RECOMMENDED" or "64 bit
IIDs are REQUIRED", depending on the context of the discussion it is
actually both.

I think we are trying to say 64 is the default subnet prefix length and IID
length, and should be used most of the time, and other non-64 subnet prefix
lengths and IID lengths can be use when necessary in special cases.
However, 64 can only be an effective default, if every implementation of
IPv6 actually supports it.

Therefore, "/64 subnet prefixes are operationally RECOMMENDED" and "all
implementations of IPv6 are REQUIRED to support 64 bit IIDs".

What Chris and I were discussing is what is the proper statement about
non-64 subnet prefix lengths and IID lengths?  I don't think non-64
lengths can be "REQUIRED" because some implementations of IPv6 only support
64 as the subnet prefix length and IID length.  This is not right or wrong,
it is just a fact we have to live with. So that leaves either "OPTIONAL" or
"RECOMMENDED" for support of non-64 lengths.  I started with "OPTIONAL" but
said I'd consider "RECOMMENDED".

Thinking about this a bit more; I think the non-64 lengths should be
"OPTIONAL for host implementations of IPv6 to support", "RECOMMENDED for
router implementations of IPv6 to support", "operational use of /127 subnet
prefixes for point-to-point router links is RECOMMENDED", and by
implication, but doesn't need to be said explicitly, the operational use of
other non-64 lengths is NOT RECOMMENDED, but not prohibited or limited in
any way either.

Thanks.

-- 
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David Farmer               Email:farmer@umn.edu
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