Re: Review of draft-ietf-6man-rfc4291bis-06

Brian E Carpenter <brian.e.carpenter@gmail.com> Fri, 13 January 2017 01:56 UTC

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Subject: Re: Review of draft-ietf-6man-rfc4291bis-06
To: Randy Bush <randy@psg.com>
References: <148406593094.22166.2894840062954191477.idtracker@ietfa.amsl.com> <m2fukqbbwv.wl-randy@psg.com> <F6953234-3F85-4E28-9861-433ADD01A490@gmail.com> <m2wpdzhncn.wl-randy@psg.com> <82245ef2-cd34-9bd6-c04e-f262e285f983@gmail.com> <m2d1frhjfn.wl-randy@psg.com>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Fri, 13 Jan 2017 14:55:59 +1300
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Cc: IPv6 List <ipv6@ietf.org>, int-dir@ietf.org, Bob Hinden <bob.hinden@gmail.com>, draft-ietf-6man-rfc4291bis.all@ietf.org, IETF <ietf@ietf.org>
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On 13/01/2017 13:50, Randy Bush wrote:
>> RFC7421 (which is Informational) calls out RFC 6164 (not 6141!) as an exception.
>> To be precise it says:
>>
>>    The de facto length of almost all IPv6 interface identifiers is
>>    therefore 64 bits.  The only documented exception is in [RFC6164],
>>    which standardizes 127-bit prefixes for point-to-point links between
>>    routers, among other things, to avoid a loop condition known as the
>>    ping-pong problem.
>>
>> I would suggest adding a similar exception statement in 4291bis.
> 
> and then next year we will go through another draft and have another
> exception.  just get rid of classful addressing.  we went through this
> in the '90s.

The problem is (and why we wrote 7421) is that stuff breaks with subnet
prefixes longer than 64, *except* for the point-to-point case covered
by 6164. Yes, I see the problem in enshrining this but I think we face
signifcant issues if we do otherwise.

What we could conceivably say is that /64 is mandatory except for
links where SLAAC will never be used. (SLAAC itself is designed
to work with any reasonable length of IID, but again in practice it
only works with /64, because we need mix-and-match capability. So
although IID length is a parameter in the SLAAC design, it's a
parameter whose value needs to be fixed globally.)

    Brian