Subject: [Autoconf] Random MLA uniqueness

From: "Teco Boot" <[email-masked]>
Date: Mon, 19 Nov 2007 23:20:39 +0100

Hi,

I was thinking on likelihood of collisions using ULA for MLA.
When using ULA random Global_ID and Subnet_ID, we have already 56 bits.
Enough for 7733248 /64 prefixes per human being (projected 2050 world
population).

For Cryptographically Generated Address (CGA, RFC3972) we have 59
crypto-random bits on Interface ID, 115 bits total.
For Randomized Interface Identifiers (RFC3041) we have 63 random bits, 119
in total.
(note that RFC4429 mentions 62 bits, reserving both U and G bits)

Lets calculate worst case, with 115 bits and a MANET with 100.000 nodes
(immense MANET).
I think we need a big supercomputer to calculate the probability for
birthday paradox;-)
It is something like Pb(2^115,100000) = 1-( 2^115! / [ (2^115-100000)! .
2^115^100000] )

RFC4429 provides a formula for the upper limit:
  Pb(n,k) <= 1-( [(n-k+1)/n] ^ [k-1] )
  Pb(2^115,100000) <= 1-( [(2^115-100000+1)/2^115] ^ [100000-1] )
I can't calculate the outcome. Has anyone a calculator with extreme long
real numbers?

Maybe the problem is in the random number generator.
Anyway, I think someone should work on address spoofing protection.
Pspoofing >>>> Pb.
Some of us will tell that their birthday is on the same day as someone else,
and they save on treat.

Adding this information in problem statement?

Teco.

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