[ppml] Proposed Policy: Proposal to amend ARIN IPv6 assignment and utilisation requirement

[Geoff Huston]

At 12:00 AM 2/09/2005, Rich Emmings wrote:
>Opposed.
>
>Does this proposal help with a short term problem, or promote the adoption 
>of IPv6?
>
>No.
>
>If utilization becomes a problem, space yet to be allocated outside of
>2000::/3 can be allocated in smaller blocks in the future, and still leave
>enough.  Done this way, justifications for the proposal in reference to
>early adopters vs latecomers are mitigated.


If the current address plan has risks of premature exhaustion, then the 
consequent question is whether these risks should be addressed now or 
later. One approach is to adopt a "wait and see" attitude, and defer 
consideration until more data is available.

This viewpoint is expressed in RFC3177:  "We are highly confident in the 
validity of this analysis, based on experience with IPv4 and several other 
address spaces, and on extremely ambitious scaling goals for the Internet 
amounting to an 80 bit address space *per person*. Even so, being acutely 
aware of the history of under-estimating demand, the IETF has reserved more 
than 85% of the address space (i.e., the bulk of the space not under the 
001 Global Unicast Address prefix). Therefore, if the analysis does one day 
turn out to be wrong, our successors will still have the option of imposing 
much more restrictive allocation policies on the remaining 85%. However, we 
must stress that vendors should not encode any of the boundaries discussed 
here either in software nor hardware. Under that assumption, should we ever 
have to use the remaining 85% of the address space, such a migration may 
not be devoid of pain, but it should be far less disruptive than deployment 
of a new version of IP." [RFC 3177]

An alternative way of expressing this perspective is that it appears to be 
premature to consider changes to the IPv6 address plan when we have so 
little experience with deployment of IPv6. It would appear that we are not 
qualified to make such decision and leave them to more qualified 
individuals. Who would they be? From this perspective they would be the 
network engineers of the future who would have had 10-20 years of IPv6 
operational experience.

Lets look at this assertion in a little more detail. Now if the consumption 
analysis in RFC3177 is indeed flawed, and uptake is larger than has been 
anticipated in the current IPv6 address plan, then yes, there will still be 
large pools of unallocated address space available, and yes, it will be 
possible, in theory at any rate, to use a different addressing plan on the 
remaining space which targets a higher utilization rate. However the 
installed base of IPv6 will also be extremely large at this point. Indeed 
it will be so large that the problem of inertial mass and potential gross 
inequities in distribution structures will effectively imply that any 
changes will be extremely tough politically.

It could be argued that we have already lived through a similar transition 
in IPv4 in the change from class-based addressing to one of classless 
addressing plus Network Address Translators. The legacy of this transition 
is uncomfortable, with later adopters pointing to the somewhat liberal 
address holdings of the early adopters and asking why they have to bear the 
brunt of the cost and effort to achieve very high address utilization rates 
while the early adopters are still able to deploy relatively simple, but 
somewhat more extravagant addressing schemes across their networks.

When to consider such a change to the address plan is very much a public 
policy topic. While there is a temptation to leave well alone, from a 
public policy perspective we stand the risk of, yet again, visibly creating 
an early adopter reward and a corresponding late adopter set of barriers 
and penalties. I suspect that IP has already exhausted any tolerance that 
may have been enjoyed in the past on this type of behaviour and there is a 
strong impetus on the part of many developing populous economies not to see 
such a precise rerun of what they would term previous mistakes. This is not 
an abstract concept but one where we are already seeing proposals from the 
ITU-T to establish an alternative address distribution system that is based 
around this particular concern of re-creating a framework that has already 
established early adopter rewards and late adopter penalties in IPv4, and 
is looking to repeat this same inequitous pattern in IPv6..

In other words it is possible to put forward the proposition that this is a 
premature discussion, but others, for equally valid reasons, see it as 
being timely, while others see this as an urgent priority. There is a case 
to be made that we should study the evolution of address policies in the 
history of IPv4 and be careful to avoid a needless repetition of earlier 
mistakes. It would appear to be prudent, and indeed "fairer" to plan for 
success rather than failure, and plan for extensive, indeed ubiquitous 
deployment of IPv6 for an extended period of time. In such a scenario there 
is little room for structural inequities in the address distribution model, 
and that at all times all players should be positioned evenly with respect 
to access to addresses. Consequently there would be little room to adjust 
the address plan parameters on the fly and we should exercise some care to 
ensure that the address plan structure we adopt at the outset has 
sufficient room to accommodate future requirements on a similar, if not 
identical, basis. From this perspective the time for consideration of the 
address plan and its associated parameters is now, rather than deferring 
the matter to some unspecified future time.

The alternative is that the installed base of IPv6 will consume very little 
address space in the coming decades, in which case the entire topic would 
be irrelevant! In other words this topic is predicated on the assumption 
that in some 50 or 100 years hence we will still be using IP as the base 
technology for a global communications enterprise.

regards,

    Geoff Huston