Subject: Re: [MOBILE-IP] MIPv6 address conflict checking?

From: "N. Asokan" <[email-masked]>
Date: Mon, 13 Dec 1999 15:58:57 +0200

[email-masked] wrote:
> => interface IDs are 64 bit long, if you remove the global bit the
> birthday standard argument give a zero probability of a collision when
> there are less than 2^(63/2) (ie 3037000500) nodes: I can
> live with this!

Just a nit: I think the birthday argument says that if there are 2^(63/2)
nodes, there will be _50%_ probability of collision.

The only way to get zero probability of collision with random assignment
is to drastically limit the number of nodes, to 1. :-)

This doesn't change the rest of you argument though.

Regards,
- Asokan

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N. Asokan, Communication Systems Lab, Nokia Research Center, Helsinki

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From: Francis Dupont <[email-masked]>
Date: Mon, 13 Dec 1999 16:36:46 +0100

In your previous mail you wrote:

=> yes, if N < 2^(63/2), probability is ~ 0%, at 2^(63/2) it is 50% and
if N > 2^(63/2) it is ~ 100%. Of course these <, = and > are not strict...

=> I've said zero probability for nearly impossible (which is more for
a continuous space than a discrete one but this doesn't change the argument).

=> the important thing is the order of the number of nodes needed in
order to get a collision...

[email-masked]

PS: 2^(63/2) is not an integer too (:-)!
PPS: draft-ietf-ipngwg-addrconf-privacy-01.txt gives a way to get a
random interface ID (and has the same kind of discussion).