# using "reserved" IPv6 space

Cameron Byrne cb.list6 at gmail.com
Thu Jul 19 14:40:31 UTC 2012

```If i may summarize this thread as a method to conclude it.

1. Some people like GUA the most.

2. Smart network operators understand the facts and make decisions based on
facts (ULA exist, and it meets a need in some scenarios. NAT and lack of
addresses are not reasons to use ULA).

3. Most FUD around ULA comes from an over-reaction to ipv4 NAT sins,
misunderstandings about how security policy works in the real world , and
deficiencies in mathmatical education.

CB
On Jul 19, 2012 5:48 AM, "Mark Andrews" <marka at isc.org> wrote:

>
> In message <
> CAAAwwbXh1wS_9aX4FwGrqmSBJmKGJ0nWHRi9EN53HtL36VhSSg at mail.gmail.com>
> , Jimmy Hess writes:
> > On 7/18/12, Karl Auer <kauer at biplane.com.au> wrote:
> > > I don't understand the professed need for provable randomness. Without
> a
> > > number *space* to provide context, randomness is inherently
> > > non-provable. The whole point of the randomness of those 40 bits of ULA
> > > infix is that any number is as likely as any other number. Someone,
> >
> > 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".
> >
> > A random generator that is operating correctly, is much more likely to
> > emit a number with 50% of the bits set to 1,   than it is to emit a
> > number with 0% of the bits set to 1, given a sufficient number of
> > bits.   If the ratio is inconsistent by a sufficient margin, and your
> > sample of the bits is large enough in number,   you can show with high
> > confidence that the number is not random;   a  1 in 10 billion chance
> > of the number being randomly generated, would be pretty convincing,
> > for example.
>
> Actually you can't.
>
>         fdaa:aaaa:aaaa has 20/20 0/1 bits but is entirely non random.
>         fdf0:f0f0:f0f0 has 20/20 0/1 bits but is entirely non random.
>
> The ratio of the number of bits doesn't tell you anything about whether
> the number was random or not.
>
> > Removing the temptation  by excluding the small number of choices with
> > 90%  - 95%  of the bits set to 1  may eliminate future problems caused
> > by an early "accident"/"error" in assigning the initial ULA,
> > compared to the minor inconvenience of needing to run the ULA
> > generator one more time to get an actual usable range.
> >
> > > somewhere, is eventually going to get 10:0000:0000, someone else will
> > > eventually get 20:0000:0000 and so on. And they are just as likely to
> > > get them now as in ten years time.
> >
> > That is extremely improbable.
> > 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.
>
>         improbable != impossible
>
> > --
> > -JH
> >
> --
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org
>
>

```