ISP customer assignments

David Barak thegameiam at
Tue Oct 6 00:22:11 UTC 2009

The fallacy here is the idea that IPv6 has a 
128-bit namespace.  It does not.  It has
 two 64 bit namespaces, where one is expected to be globally unique and flat, 
While the other is hierarchical.

IPv6 has a lot more room than v4 does, but it is worth noting
Than in v4, a customer would typically use a single /32.  In v6-speak, a /48 is a smaller percentage
of the overall space, but it would not be 
prudent to view the v6-space as infinite.  Remember, 
the value of a network increases with the number of interconnections,
and those interconnections are what get numbered.
All of the comparisons to atoms in the galaxy or human population are ignoring the hierarchical element
of the 64-bit space.  The nature of hierarchical allocations requires a 
Significant "burn" in terms of wasted, unusable addresses.

All that said, the /64-based v6 addressing 
approaches are going to be with us for quite a while,
so they're worth getting used to.

-David Barak

David Andersen wrote: 
> On Oct 5, 2009, at 7:50 PM, Michael Thomas wrote:
>> I'm perplexed. At what size address would people stop worrying about
>> the "finite" address space? 256 bits? 1024 bits?
>> I just don't get it. It's not like people get stressed out about running
>> out of name space in English which is probably more "finite" than ipv6.
> Unless you're trying to find a nice, catchy, short domain name. ;-)
> But seriously:  Many people don't seem to have good intuition about really big numbers.  Say, on the order of 2^128.  The same thing comes up in discussions about hash collisions in, e.g., content based naming with a 160-bit namespace.  I think it's because the numbers are so astronomically big, that without some amount of math and having thought about it with paper and pencil, people automatically scale the #s into terms they can think of as "really big" (like, # of people on earth).  So when they think about the 128-bit namespace, they apply intuition that works for a 35-bit namespace...
>   -Dave


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