Re: IPv6 address space shortages (was: Re: A simple question)
2003-04-29 14:28:26
Dean,
Since you have responded to a comment of mine, let me summarize
my reasoning with regard to the "out of IPv4 address space"
problem. Your assumptions, views, definitions, religion, etc.,
may differ.
--On Tuesday, 29 April, 2003 15:28 -0400 Dean Anderson
<dean(_at_)av8(_dot_)com> wrote:
We are still not out of IPv4 address space. I don't know the
projections for address space depletion,
One view of "address space depletion" is that projections are
useless in an environment in which (i) the RIRs believe that
their job is to prevent us from running out of space and (ii)
they are good at their work. Those two statements imply that
policies will adjust as they perceive we are getting closer to
running out of space and, in turn, two seemingly-contradictory
statements about the date on which we run out of IPv4 space:
(1) We will _never_ run out of IPv4 space, but you
really don't want to be the entity that asks for the
next-to-last block (or any other block after your local
RIR starts feeling significant end-game pressure).
I.e., while we won't run out, getting space with get
more and more expensive and/or aggravating, going up by
step functions.
(2) Given that model, it is more appropriate to look at
the date at which it gets sufficiently difficult to get
unique, globally-routable space (note that I did not say
"PI") that people with a legitimate requirement for it
perceive themselves as being unable to get it, or enough
of it to meet their requirements. Even 1918 recognizes
that there are hosts that should have public addresses.
To the extent that policies about IPv4 allocations are
forcing such hosts behind NATs --or substitutes the
judgment of RIRs or ISPs about what should, and should
not, be public for that of local network
managers/designers, or make it economically implausible
to have public hosts-- then we have already passed that
date. And, to oversimplify things somewhat, it is
accurate to say that we have already run out of space,
because a rational criterion for "run out of space" is
that it forces us into architecturally pathological
behavior.
but I think the IPv6
problem won't be so much address space depletion as route
space depletion. I think it will be unwieldy to have a million
or 2 million or 10 million distinct routes.
Many of us agree with you, at least within the constraints of
the current routing regime and models. But the question, on one
side, is how to organize IPv6 allocations so that we don't have
that problem. One theory is "almost no PI space except in very
large aggregates, multiple (provider-dependent) addresses per
host. As far as I can tell, that is the path we are going down.
But it involves a number of tradeoffs which have, perhaps, not
been explored and articulated as well as is desirable. One of
them is that the strategy uses up addresses faster than the
network grows (in host counts), even while it may conserve
routing space. If you can anticipate the possibility of an RIR
eventually telling an ISP "you can't count networks in your
request for a larger allocation if they already have addresses
from another provider", then we are in danger of being "out of"
IPv6 address space coming out of the gate -- and that is one
example of the motivation behind my challenge to Bill... and
perhaps even of his "yet" comment which led to my challenge.
Aggregation won't
happen the way things are currently organized.
Maybe. See above.
<soapbox> I think the RIRs (at least for IPv6) need to be
organized differently. In order for address space to be
hierachical, for efficient aggregation and routing, addresses
have to be given out locally, like phone numbers.
Unfortunately, that isn't how ISP's or the address registries
are organized. Fees are strongly biased towards big companies,
yet the small and medium sized companies generate most of the
revenue. It costs way too much money to get IPv6 space for
every town to have their own address space, so that even barn,
cow, and coke machine can be connected to the internet.
Something needs to give. </soapbox>
Your conclusion may be right, but I don't think the reasoning in
the paragraph above works. Let me restate it to see if I can
explain why.
The only way we know for address space to be efficiently
aggregated and routed is to make it hierarchical, and for that
hierarchy to reflect routing realities. Unless we either change
the business models of the industry, or create the type of
regulatory regime that characterized the PSTN a few decades ago
(which may be just one form of changing the business models),
the hierarchy has to follow provider topologies and
interconnection structures.
It makes sense for every town to have its own address space only
if every town has a sufficient number of exchange/
interconnection points with other towns, or backbone providers
of one sort or another to give the town global connectivity.
But, in the general case, that is going to require a regulatory
regime -- it isn't obviously in the interest of the ISPs, either
technologically or economically, to make things work that way.
Of course, "address space per country" and, typically, address
space per entity within country, is exactly the way address
allocations work in the PSTN under the E.164 Recommendation/
System. But, if that type of address structure is to be used
for routing, it depends on a collection of bilateral agreements
(and exchange points) between countries, plus local and national
routing regimes that are traditionally highly regulated (today's
"deregulated" environment depends on the previous regulatory
structure in a number of important ways), involve specialized
and sometimes subsidized exchange points, small numbers of
interexchange carriers relative to the number of exchanges (or
event "towns"), etc.
I don't think we want to go there, but your opinions may, again,
differ.
john
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