[address-policy-wg] Policy proposal: #gamma IPv6 Initial Allocation Criteria

> If these policies cause 2000::/3 to be exhausted then there are 7 more
> tries left to do it all over again.

This is the essential characteristic of IPv6 that so many 
of us, weaned on IPv4, seem to forget. We need to keep this
fact uppermost in our minds at all times. Even this subset
of IPv6 is much bigger than the IPv4 space. So we can afford
to be generous and, in fact, we can afford to make mistakes.
If we err, we should err on the side of being slightly too
generous because if 2000::/3 runs out, we can try again,
older but wiser.

This means that we should not be excessively concerned with
conserving address space or wasting addresses. It is entirely
appropriate to give a /32 to anyone who might be some sort
of an ISP, either traditional or some new type, like Google
or BMW or Cadburys. It is entirely appropriate for these
ISPs to give a /48 to every customer except in the very
unusual situation where a customer connects with only a
single device that has a single network in it. The only such
situation that I can think of is a mobile phone.

However, we should not stop thinking about conservation. This
is the real world and we do have limitations in router hardware
and memory chip capacities and speeds. It would be foolish
to allow the routing table to grow without bounds. This is 
where we need to be conservative and make policies which are
not wasteful of routing table space.

Now, a set of IPv6 policies in which no globally routable
prefixes are longer than /32 allows router manufacturers 
to optimize memory usage and design router tables to only
carry those 32 bits of the IPv6 address. This will conserve
memory and allow the routers to scale easier. Of course,
any such design will impose a computation penalty on prefixes
longer than /32, i.e. /8 prefixes, and that would make it
inappropriate to announce /48 prefixes globally for things
like DNS infrastructure.

Note that I am not interested in whether or not current router
implementations or BGP implementations support truncated
prefixes in order to realize savings of memory, bandwidth,
transmission time, or computation time. That is not our job.
Our job is to make a sensible policy that allows the use of
IPv6 to scale smoothly so that it meets the needs of humankind
for the next generation or two. Let's not be so arrogant that
we try to solve all addressing problems forever. That is not
necessary. There will be people who come after us and if they
feel that we botched the job in 2000::/3, then they have the
opportunity for a much easier transition than the transition
from IPv4 to IPv6. 

--Michael Dillon