[ppml] 2005-1:Business Need for PI Assignments

Michael.Dillon at radianz.com Michael.Dillon at radianz.com
Mon Apr 25 11:31:42 EDT 2005

> A /32 of IPv4 space is the same percentage as a /32 of IPv6 space. 
> That's obvious.  So what?  With more address space available, I would 
> expect to get a smaller percentage of the overall space.

You do! There are only a few ISPs, mostly in 3rd world countries,
who have to make do with only a /32 of IPv4 space. Conversely, in IPv6,
there are only a few ISPs who need more than a /32 of IPv6 space.

> What I'm afraid I am hearing is that "since there are so many more 
> IPv6 addresses, let's loosen the address supply to make it easier to 
> manage."  That sounds a little like a cop out, understanding that the 
> technology is immature and we don't really know where it's heading.

Not at all. I am not suggesting that we "loosen" the address supply.
The characteristics of IPv6 (larger address space, allocation of
/48 to stub networks) have naturally resulted in a much tighter set
of rules in which the majority of ISPs will receive only a /32 of
space. This is much, much less than what we give ISPs from the IPv4

> If you put a /48 in my house, with each device getting a /64 to 
> assign a /128 to it's interfaces, I still have a hard time imagining 
> that this would be an efficient use of space.

Now you are thinking like a Bedouin in the Sahara. When water is scarce
and you must travel many days to reach a water source, then it seems like
incredible waste to use water for washing. You have a hard time imagining
that people anywhere could justify the use of water for washing their
bodies. But in the interior of British Columbia, in a semi-desert area
called the Okanagan Valley, people who live along the shores of a large
freshwater lake fed by mountain glaciers have a rather different 
As do the residents of Seattle, where it is not unusual for the rain to
fall for days without stopping.

The question of waste has to do with the environment you are in, the 
of supply, and the difficulty of obtaining a resource. IPv6 addresses may
be finite in number, like water molecules on this planet, but they are
as numerous as the raindrops which fall on the western rainforests of
North America.

It would be inefficient for a resident of Seattle to live in a tent, 
himself to 5 liters of water per day for drinking and cooking and only 
himself in a public shower facility. Unless, of course, he is on a trip in
the north Sahara. Similarly, it is inefficient for users of IPv6 addresses
to try to design their networks to conserve addresses according to IPv4 

> Even with MIT-like 
> smart kitchens, etc., I can't imagine that much address space being 
> needed and used efficiently.

No doubt most Bedouins cannot imagine why an American needs 5 gallons
to flush the toilet. This is the daily water ration for 4 adults on
trek in the north Sahara!

> It seems to me that IPv6 DHCP assigning addresses more compactly than 
> using  the Ethernet address as the last 48 bits would be worth the 
> management overhead.

You are at liberty to run your home network the way that you want to
but when we make IPv6 addressing policy we have to do it in the context
of the IPv6 RFCs in which it is mandatory to assign a /48 to any
stub network unless it needs more addresses. We can't change that. Our
policies have to deal with allocations of blocks larger than /48 in size
to network operators who then assign /48 out of their allocation.

--Michael Dillon

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