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

Lorenzo Colitti <lorenzo@google.com> Wed, 18 January 2017 07:42 UTC

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From: Lorenzo Colitti <lorenzo@google.com>
Date: Wed, 18 Jan 2017 16:42:19 +0900
Message-ID: <CAKD1Yr2AxiyXSM4DNSOMJAkCT610pjkvczpQtKS-=j7SfWRjGg@mail.gmail.com>
Subject: Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]
To: Fernando Gont <fgont@si6networks.com>
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On what link type? On Ethernet, RFC 2464 clearly defines the IID length to
be 64 bits, period. So /64 is correct.

If there's an IPv6-over-foo document that does not specify the IID length,
then the IID length is unspecified. Because it's unspecified, whatever they
pick is fine. "Do nothing" or "use /64 for consistency with global
addresses" would be the most obvious choices.

On Wed, Jan 18, 2017 at 11:04 AM, Fernando Gont <fgont@si6networks.com>
wrote:

> 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
>
>
>
>
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