[manet] Re: BABEL question

That gives you a number in the right ballpark. But not the exact answer if you just divide one by the other as the pairs (or the equality of the pairs) aren’t independent.

> On 24 Jul 2025, at 23:10, Donald Eastlake <[email protected]> wrote:
> 
> I believe that, due to the so called "Birthday Paradox", If you select
> 2**32 (about 4.2 billion) values from a pool of 2**64 values with
> replacement, the probability of a conflict among the selected values
> 50%. https://en.wikipedia.org/wiki/Birthday_problem The thing is that
> to determine whether there is a conflict, you need to compare all
> unordered pairs. With N items, the number of pairs is N*(N-1)/2 so the
> number of cases of possible conflict goes up with the square. The
> number of unordered pairs of 2**32 things is ~2**63.
> 
> Thanks,
> Donald
> ===============================
> Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
> 2386 Panoramic Circle, Apopka, FL 32703 USA
> [email protected]
> 
>> On Thu, Jul 24, 2025 at 5:51 PM Juliusz Chroboczek <[email protected]> wrote:
>> 
>>> Imagine a prefix like: "2001:db8:f000::/48" where the lower 16 bits of
>>> the /64 do not represent a subnet ID but instead identify a host route
>>> delegation service.
>> 
>> I most respectfully disagree.
>> 
>> I have no objection to defining a flat prefix of MANET interface
>> addresses.  However, the prefix must be flat, as anything else is
>> gratuitious complexity that doesn't bring any practical benefits.
>> 
>> (Henning is right, by the way, a /64 is good enough.  If I recall my
>> undergrad combinatorics correctly, a /64 gives a vanishingly small
>> probability of collision when the total number of nodes is less than
>> 4.2 billion.  For a /48, the value is roughly 10¹².)
>> 
>> -- Juliusz
>> 
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