From: Thomas Narten [mailto:narten@xxxxxxxxxx]
Sent: Tue 28/08/2007 4:13 PM
To: John C Klensin
Cc: ietf@xxxxxxxx
Subject: Re: IPv6 addresses really are scarce after all
Hi John.
> Let me suggest a slightly different perspective on this.
> First, the decision as to how large to make the IPv6 address
> space is, and was, an architectural decision. We could have
> chosen a longer length, we could have chosen a shorter one, we
> could even have made it variable length (with or without a
> fixed-length or maximum-length network part). As others have
> pointed out, we could have taken explicit measures to separate
> IP-level addressing from routing as a fundamental part of that
> architecture. All of those options were considered (although
> some a lot more carefully than others).
> Whether it is obsolete or not, and, if it is, whether because of
> hardware or security considerations, the belief that local
> networks needed to have 64 bits available for MAC address
> mapping were also part of that picture. Again, certainly an
> architectural decision rather than "pure policy".
> Whether it was explicit or not, assumptions about the effective
> size of that address space -- how many sites or "networks" it
> could serve -- were also part of those architectural decisions.
> I remember a whole series of discussions about whether N bits
> (for various values of N) were enough under various scenarios.
> We might not have gotten those decisions right, but they were
> IETF decisions and decisions made as part of determining what
> IPv6 looked like.
Agreed.
But I think there was a lot more discussion about this in the very
early days, when 128 bits was chosen, and when stateless address
autoconfiguration assumed that the Interface Identifier part of an
address was 48 bits, leaving 64+16 bits for routing.
Then, we made the decision to make Interface Identifiers 64 bits,
shrinking the routing part to 64 bits.
I agree completely that the /64 boundary was/is architectural. For
better or for worse, stateless address autoconfiguration (as currently
specifies) only works on links that have a /64 assigned to them.
But the /48 boundary is not. We had a long discussion about that in
the IPv6 WG, and our specs were carefully cleansed to make sure there
were no real dependencies on such a boundary. Think Randy Bush saying
"your reinventing IPv4 classful addressing" about a thousand
times. :-)
Indeed, even though the official IETF party line is that links have to
have 64 bits of subnet addressing assigned to them, a number of
operators screamed loudly that for internal point-to-point links, that
was horribly wasteful and they weren't going to stand for it. So,
products do indeed support prefixes of arbitrary length (e.g., /126s
and the like), and some operators choose to use them. This is one of
those situations where the IETF specs seem to say one thing, but the
reality is different. And we pretend not to notice too much.
> Second, the notion that RIRs set addressing policy is one that
> has not been in place forever. Indeed, it has evolved very
> slowly and mostly by assertion by the RIRs that they have that
> authority --assertions that, in other contexts, might look a lot
> like either filling a vacuum or turf grabs depending on one's
> perspective. While they have always (since there have been
> RIRs) had broad discretion within their own regions, and it has
> always been recognized some coordination discourages
> forum-shopping and other bad behavior, global address policy was
> historically set by IANA in conjunction with the IAB, not by the
> RIRs (although I assume their advice was certainly welcomed).
Understood. But I think the reality today is that we have the world we
live in and serious suggestions to overturn the current world order
better have a strong and compelling motivation.
I'm sure you've also noticed, but IANA's recent position seems to be
more like "IANA doesn't make policy, IANA does what the community asks
of it".
> Without taking any position on whether the ARIN decision is a
> reasonable one, I believe that the IETF has had, and continues
> to have, a role in the general design of addressing
> architectures and hence in allocation strategies. I also
> believe that the RIRs have some obligation to consult the IETF
> before making a major policy change and to pay careful attention
> to anything rational the IETF has to say. I also believe that
> things are seriously out of joint if we need to worry about
> whose toes are being stepped on before opinions are expressed.
I think that has mostly been happening, though it could always be done
better. The proposed changes to the HD ratio and /48 boundary were
certainly discussed in the IPv6 WG when they took place. And there are
folk that participate in both the IETF and the RIR communities.
Thomas
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