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

[Fernando Gont <[e-mail]>]

On 01/17/2017 09:16 PM, Manfredi, Albert E wrote:
>> -----Original Message----- From: ipv6
>> [mailto:[e-mail]] 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: [e-mail]
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