[arin-ppml] A modest proposal for IPv6 address allocations

michael.dillon at bt.com michael.dillon at bt.com
Fri Jun 5 19:01:12 EDT 2009

> To eliminate the games, you standardize, but that has its own 
> problems. RFC 3177 has already decided that every cellphone 
> "needs" 18,446,744,073,709,500,000 host addresses. That, 
> patently, isn't true; many thousands of trillions of 
> addresses will be wasted because end sites don't need them. 

You should eliminate your games. That is patently not true.
RFC 3177 says: 

   It is not obvious, however, that all edge networks are likely to be
   recursively subnetted; a single PC in a home or a telephone in a
   mobile cellular network, for example, may or may not interface to a
   subnetted local network.  When a network number is delegated to a
   place that will not require subnetting, therefore, it might be
   acceptable for an ISP to give a single 64-bit prefix - perhaps shared
   among the dial-in connections to the same ISP router.  However this
   decision may be taken in the knowledge that there is objectively no
   shortage of /48s, and the expectation that personal, home networks
   will become the norm. 

Then later:

   Mobile networks, such as vehicles or mobile phones with an
   additional network interface (such as bluetooth or 802.11b)
   should receive a static /64 prefix to allow the connection of
   multiple devices through one subnet.

It never talks about huge numbers of host addresses. And it
does reference RFC 2374 which explains how interface ids are 
constructed which makes it clear that the minimum subnet 
size is a /64. No addresses are wasted. Some bit combinations
are never used but that is not waste, since neither IPv4 or
IPv6 is architected in a way that all bit combinations could
be used for endpoint addresses.

> Making finer distinctions requires massive investments in 
> organizational overhead: reviews, monitoring, etc.

Precisely the justification for having standard prefix lengths
of /64, /48 and /32 in the first place. It massively cuts 
down the overhead of having to make fine grained measurements
of subnet size, carefully mete out small address blocks, and
then restructure everything when some part of the network 
outgrows its address allocation. IPv4 wastes money, but IPv6
leverages a much longer bitstring to cut out that waste in
overhead, monitoring, reviewing and restructuring the network
to accomodate growth.

--Michael Dillon

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