Re: Last Call: <draft-ietf-6man-rfc4291bis-07.txt> (IP Version 6 Addressing Architecture) to Internet Standard

神明達哉 <jinmei@wide.ad.jp> Thu, 23 February 2017 18:45 UTC

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Date: Thu, 23 Feb 2017 10:45:44 -0800
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Subject: Re: Last Call: <draft-ietf-6man-rfc4291bis-07.txt> (IP Version 6 Addressing Architecture) to Internet Standard
To: Lorenzo Colitti <lorenzo@google.com>
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Cc: draft-ietf-6man-rfc4291bis@ietf.org, 6man-chairs@ietf.org, 6man WG <ipv6@ietf.org>, IETF-Discussion Discussion <ietf@ietf.org>
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At Thu, 23 Feb 2017 13:16:46 +0900,
Lorenzo Colitti <lorenzo@google.com>; wrote:

> Help he understand, then. There is widely-deployed code that assumes that
> the interface ID is 64 and does not work on anything other than 64 bit
> prefix lengths.

Out of curiosity: which code is it, and exactly what does its
assumption mean?  Does it mean, for example, it allows manual
configuration of an address but requires its IID length be 64 bits?
(If it means something like this, I'd also wonder how its "IID"
matters in the first place - does that implementation use the lower 64
bits for some specific purpose?)

I thought general-purpose OSes are actually quite flexible about the
length of "IIDs" (in many cases it's actually derived from the length
of on-link prefix corresponding to the address).  I know BSD variants
are intentionally flexible on this.  I also know at least some (if not
all) kernel versions of Linux are flexible.

The only example of "widely-deployed code" with such an assumption
that I know of is ISC DHCPv6 client (though I'm not sure if its latest
version still has that assumption) as described in Section 4.4 of
RFC7421.  But I guess you're referring to something else.

If you can be more specific it might help provide some clarity for the
discussion, although I'm not so optimistic that it will automagically
resolve the conflicting views we are seeing.

--
JINMEI, Tatuya