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

Brian E Carpenter <brian.e.carpenter@gmail.com> Sat, 25 February 2017 22:22 UTC

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Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
To: David Farmer <farmer@umn.edu>
References: <20170223134026.GI5069@gir.theapt.org> <9277BC0B-04F3-4FC1-901E-F83A8F0E02D7@google.com> <58AF6429.70809@foobar.org> <902276E9-0521-4D4E-A42B-C45E64763896@google.com> <58AF726A.3040302@foobar.org> <F7C230DE-4759-4B78-ABF2-6799F85B3C62@google.com> <58B014F6.2040400@foobar.org> <6DA95097-8730-4353-A0C9-3EB4719EA891@google.com> <CAN-Dau0s04c=RV0Y8AGaxBPFui41TWPTB+5o0K2Lj-iah0An1w@mail.gmail.com> <CAL9jLaYirty22iGiEjEaYq3_KA1FZhxBTOBWuFOXQ9C-WPd5xQ@mail.gmail.com> <CAN-Dau0n6oFm538XdJOcuO1yg92BCDD3mBu5YfBVm_+g-gtcKA@mail.gmail.com> <CAL9jLaYO=uYgVfSZ0SoSe0SujJ1xgwEKE8WLzo_keJHywgXTtg@mail.gmail.com> <CAN-Dau1vJV5O_Ythp6THkAu4-YZXV82Upny1V+ybbjCVZQQX=A@mail.gmail.com> <27cce319-18ac-5c0e-3497-af92344f0062@gmail.com> <de4988be-6031-08d9-84ce-21c3fa4f9bc9@gmail.com> <CAN-Dau0fq9eU71Od3oq9DRq1qLLMqiW-gr-oxgkc46Xo6hjE+Q@mail.gmail.com>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Sun, 26 Feb 2017 11:22:07 +1300
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Cc: Alexandre Petrescu <alexandre.petrescu@gmail.com>, 6man WG <ipv6@ietf.org>
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On 26/02/2017 09:40, David Farmer wrote:
> 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.

In the context of *this* thread about the addressing architecture, I don't
think we should say much at all. Most of what you say belongs IMHO in a
separate, and quite short, operational BCP.

   Brian