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

Lorenzo Colitti <lorenzo@google.com> Mon, 23 January 2017 13:37 UTC

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From: Lorenzo Colitti <lorenzo@google.com>
Date: Mon, 23 Jan 2017 22:37:27 +0900
Message-ID: <CAKD1Yr2jFf=OFiCJLWV48FRZF1iuWK1mLJ9+kQiuFBxujgCOBQ@mail.gmail.com>
Subject: Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]
To: Tore Anderson <tore@fud.no>
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On Mon, Jan 23, 2017 at 8:49 PM, Tore Anderson <tore@fud.no> wrote:

> > As explained before, there is no conflict between RFC 4291 and RFC
> > 7608. RFC 7608 applies to forwarding, RFC 4291 applies to link
> > addressing. I don't see a conflict between RFC 5942 and RFC 4291. Can
> > you clarify what you mean?
>
> Isn't there a conflict with RFC 6052, though?
>
> E.g., if you're using an RFC 6052 NSP such as 2001:db8:6052::/96, the
> IPv4-translatable representation of an IPv4 subnet such as 192.0.2.0/24
> would be 2001:db8:6052::192.0.2.0/120 (2001:db8:6052::c000:200/120) and
> nodes in this subnet/link would necessarily have 8 bit long IIDs. Right?
>

I'm not sure it makes sense to draw that conclusion.

If you follow that reasoning, /96 might make sense, but all the other RFC
6052 prefix lengths don't really make sense. For example, if the NSP is 64
bits, how long would the IID be? If you say 8 bits, then that means there
are 2^40 addresses routed to the same host, which means that the prefix
length (88) plus the IID length (8) does not add up to 128. And if you say
48 bits, then that means that a host has 2^40 interface IDs for the same
interface, so the interface ID isn't really an ID any more.