Puzzeling about IPv6

Matthew Seaman m.seaman at infracaninophile.co.uk
Sat Nov 19 19:07:06 UTC 2011

On 19/11/2011 18:47, 夜神 岩男 wrote:
>> Oh, and given you've got 64bits to play with, so long as your random
>> numbers are up to scratch no need to worry about collisions.  You'ld
>> need to be assigning millions of addresses before you ran into that
>> problem.
> Not to be an ass and this is likely a decade too early, but... this is
> direct echoes of what I heard 20 years ago.
> Does systematic thinking belong in /32+ IPv6 addressing or is it in fact
> safe to just random it all away willy-nilly?

Look at http://en.wikipedia.org/wiki/Birthday_paradox

With 64bits of host address space in a typical IPv6 network, you would
need to be allocating 6.1 million addresses to have a 1 in a million
chance of a collision.  You'ld need 5.1 billion addresses for a 1 in 2
chance of a collision.  If you get a collision in a typical network of
maybe several hundred machines, then suspect your random number
generator before anything else.



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
JID: matthew at infracaninophile.co.uk               Kent, CT11 9PW

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