[arin-ppml] V6 address allocation policy

Owen DeLong owen at delong.com
Sun Jan 17 21:27:56 EST 2010

On Jan 17, 2010, at 7:46 AM, William Herrin wrote:

> On Sat, Jan 16, 2010 at 7:55 PM, Owen DeLong <owen at delong.com> wrote:
>> On Jan 16, 2010, at 4:28 PM, Michael Richardson wrote:
>>>  If techies need to get their managers to approve a checque to ARIN,
>>> the manager tells them to use IPv4 + NAT.  If the techies do not have to
>>> ask, then they will deploy IPv6 for internal use.
> No joke on that. Three years ago my boss turned me down on deploying
> IPv6 in my spare time at work on the grounds that there were wiser
> ways to spend the $1250.
>>>  (ULA buys you nothing compared to net-10)
>> 1.      ULA buys you a great deal more than RFC-1918.  ULA is statistically,
>>        if not globally unique.
> Not exactly... The analysis in RFC 4193 (ULA addressing) section 3.2.3
> is technically correct but it may be an example of "lies, damn lies
> and statistics."
> First, though de-emphasized in the RFC, the probability of collision
> has a phenomenal growth rate: two orders of magnitude for ever one
> order of magnitude increase in the number of ULA IDs. So you close in
> on a 100% chance of collision not at 2^40 IDs as you'd expect but at
> merely 2^20.
So for every 2 companies merging, you run the risk of a 1:2^20
collision.  Now, let's look at those odds in numbers more meaningful
to people... 2^20 is 1024^2, or, 1,048,576, so, the odds are, literally
not quite as good as 1 in a million of any two companies colliding.

I would argue that the odds of a collision in RFC-1918 are a lot closer
to 1:3 at best since almost everyone uses at least one of, or (or some supernet thereof).

So, in order for ULA to buy you nothing, you'd have to be able to argue
that 1:3 and 1:1,048,576 are equivalent risks. If you are willing to make
bets like that, I want to be your bookie.

> Second, consider the way folks tend to behave. Each private network
> built for whatever purpose in a particular company will consume one or
> several ULA IDs. That's each private network in each project at each
> branch of a company. A large company may well have consumed hundreds
> if not thousands of ULA IDs introducing another four to six orders of
> magnitude increase in the probability of collision when two such
> companies want to connect.
Even if this is true (I'm not completely convinced), you're comparing
ULA at 1:100<n<1000 vs. RFC-1918 at 1:0.003.

> Practically speaking, we should start to see anecdotes about ULA
> collisions as folks try to connect 100 to 1000 organizations together,
> still a usefully large number but far fewer than RFC 4193 implies.
Practically speaking, even if you buy into that argument, you're still
quite a bit better off than RFC-1918.

1.	The odds of a collision are still about 300,000 times better.
2.	The percentage of hosts likely to be affected by such a
	collision is orders of magnitude better than RFC-1918.
3.	The above all assumes not using the SIXXS ULA registry
	to keep your ULA addresses unique.


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