Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]

Fernando Gont <fgont@si6networks.com> Wed, 18 January 2017 02:11 UTC

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Subject: Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]
To: "Manfredi, Albert E" <albert.e.manfredi@boeing.com>, Brian E Carpenter <brian.e.carpenter@gmail.com>, "ipv6@ietf.org" <ipv6@ietf.org>
References: <148406593094.22166.2894840062954191477.idtracker@ietfa.amsl.com> <fcf580ec-3617-ca5f-5337-37acb6e928ba@gmail.com> <CAKD1Yr25zNeQGvNJa=WzCjKMd9LaYrSwG=o4tUWn1Zc2ASZjrA@mail.gmail.com> <93700502-5d49-86ce-11b0-ab9904423961@gmail.com> <CAKD1Yr3wyza0_enWErMhmKKkA1ZOXPv5GG8dMT8HUQZsB5--UQ@mail.gmail.com> <CAAedzxppi5g_S05-m+B2jKMYePapPM0_wMA4XioYgwipwbKVHQ@mail.gmail.com> <CAAedzxoY6MGyvzDvUcZ44ka=5RcGwQ16fzRp29445Pa7mQYNHA@mail.gmail.com> <CAN-Dau36r2UgXPfdcdEAJ914QqvVvjGJK+=mgE9Y2tpBiDSRig@mail.gmail.com> <CAKD1Yr3RpUaNKkyTPHPWWew80cyGkiT1p7vYwfejESP4tQw31A@mail.gmail.com> <CAN-Dau0OsD4RcVUN+me98g6SJ=oaAr4HoqGtP88PTbMU_-kuGQ@mail.gmail.com> <00D1565E-7119-4C52-AF06-95E3F4C5905A@employees.org> <CAN-Dau0Fkb-M8VM9iL9xwy89bir5PhNHJ3D1VFrnNppVXNyeOg@mail.gmail.com> <562C040F-EC30-49C6-849F-F63BA22233C7@employees.org> <595c73ef-ffa4-6f9e-d810-c37ea8dc2c0d@gmail.com> <5c9ea94a40bf4d95b6656debfe24f69b@XCH15-06-11.nw.nos.boeing.com>
From: Fernando Gont <fgont@si6networks.com>
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On 01/17/2017 09:16 PM, Manfredi, Albert E wrote:
>> -----Original Message----- From: ipv6
>> [mailto:ipv6-bounces@ietf.org] On Behalf Of Brian E Carpenter
> 
>> I think that the discussion on the IETF list has already shown that
>> there is no consensus for the current text. I don't agree with it
>> any more, either. It hides the tension between CIDR and the
>> consistent length needed for SLAAC.
>> 
>> Hence I'm still proposing that we change it. I think the median
>> view at the moment is for the version that runs
>> 
>> ...  For all currently allocated unicast addresses, except those
>> that start with the binary value 000, that length should be 64
>> bits.
> 
> I think that as things are today, for unicast addresses allocated
> that may use SLAAC, the "should" might not be strong enough. We have
> no other implementation of SLAAC, other than one that uses 64-bit
> IIDs. But I agree with you, when you said that future implementations
> may not require 64-bit IIDs for SLAAC.
> 
> But I completely concur with your point about tension with CIDR. In
> fact, one thing that has always bothered me about the wording "all
> currently allocated unicast addresses, except those that start with
> the binary value 000," is that it sounds like the 64-bit IID rule
> holds for the majority of the unicast address space. But that's not
> true. Only 1/8 of the total address space is "currently assigned to
> unicast," and a subset of that 1/8th has the stipulation that the
> IIDs can be of any length.
> 
> But the majority of the unicast address space is unconstrained, as it
> should be. Somehow, it always ends up sounding the 64-bit IID is a
> fixture, in most IPv6 unicast.

Has anyone tred what happens if a prefix from::/3 is advertised for slaac?

I wouldn't be surprised if, if we happen to want to use non-64 IIDS for
::/3, we find that we cannot because this 64-bit value is hardcoded
everywhere.

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492