using "reserved" IPv6 space

Karl Auer kauer at
Thu Jul 19 05:16:33 UTC 2012

On Wed, 2012-07-18 at 23:40 -0500, Jimmy Hess wrote:
> When numbers are selected by choosing a random value;  certain ratios
> of bits set to "1" are more likely to occur than other ratios of bits
> set to "1".

True. But you cannot tell, from a sample of one number, whether that
number was chosen randomly. You can only test it statistically within a
series. A particular number may be random in one sequence, non-random in

> > somewhere, is eventually going to get 10:0000:0000
> That is extremely improbable.

Yes. It's just exactly as improbable as *any other prefix* thrown up by
your favourite RNG.

> If you generate a million ULA IDs a day,  every day, it is expected to
> be over 1000 years before you generate one of those two.

The same is true of *every prefix generated*, yet amazingly, people are
generating new, unique random prefixes every day, and each and every one
of them was just as improbable. Fancy that!

It might be that long before you *expect* to see one, but that doesn't
mean you will definitely have to wait that long. It could come along
tomorrow. That's what "random" means.

Let people choose and use whatever ULA prefixes they like. That is the
*point* of ULA. If they choose poorly, then they choose poorly - it's no
skin off anyone's nose but theirs. If *I* have to choose, I will choose
a random prefix, so that in the unlikely event that I have to deal with
them, my pain will be minimised.

But the best way to win is not to play the game - use PI address space
instead of ULA.

Regards, K.

Karl Auer (kauer at

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Old fingerprint: DA41 51B1 1481 16E1 F7E2 B2E9 3007 14ED 5736 F687
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