Re: IPv6 fc00::/7 — Unique local addresses

[Owen DeLong <owen () delong com>]

On Oct 20, 2010, at 5:29 PM, Mark Smith wrote:

> On Wed, 20 Oct 2010 19:39:19 -0400
> Deepak Jain <deepak () ai net> wrote:
>
> > > Use a pseudo random number, not follow bad examples. Where are these
> > > examples? I'd be curious as to what they say regarding why they haven't
> > > followed the pseudo random number requirement.
> > >
> > > > Use something like fd00::1234, or incorporate
> > > > something like the interface's MAC address into the address? It'd
> > > make
> > > > the address quite unreadable though.
> > > Unique Local IPv6 Unicast Addresses
> > > http://tools.ietf.org/rfc/rfc4193.txt
> >
> > [snipped a bunch of stuff above]. 
> >
> > According to the RFC: 
> >
> > 3.2
> >
> >   The local assignments are self-generated and do not need any central
> >   coordination or assignment, but have an extremely high probability of
> >   being unique.
> >
> > 3.2.1.  Locally Assigned Global IDs
> >
> >   Locally assigned Global IDs MUST be generated with a pseudo-random
> >   algorithm consistent with [RANDOM].  Section 3.2.2 describes a
> >   suggested algorithm.  It is important that all sites generating
> >   Global IDs use a functionally similar algorithm to ensure there is a
> >   high probability of uniqueness.
> >
> >   The use of a pseudo-random algorithm to generate Global IDs in the
> >   locally assigned prefix gives an assurance that any network numbered
> >   using such a prefix is highly unlikely to have that address space
> >   clash with any other network that has another locally assigned prefix
> >   allocated to it.  This is a particularly useful property when
> >   considering a number of scenarios including networks that merge,
> >   overlapping VPN address space, or hosts mobile between such networks.
> >
> > ----
> >
> > Global ID in this case means the 40 bit pseudo random thing. The point here is, we are all supposed  to pick our own 
> > poison and pray that we are unique.
>
> The chance of collision is dependent on both the randomness of 40 bits
> *and* how interconnected the ULA domains are. You'll have to sin a lot to be that unlucky.
>
> Here's the table from the RFC showing the odds of collision based on interconnectedness -
>
> The following table shows the probability of a collision for a range
>   of connections using a 40-bit Global ID field.
>
>      Connections      Probability of Collision
>
>          2                1.81*10^-12
>         10                4.54*10^-11
>        100                4.54*10^-09
>       1000                4.54*10^-07
>      10000                4.54*10^-05
>
>   Based on this analysis, the uniqueness of locally generated Global
>   IDs is adequate for sites planning a small to moderate amount of
>   inter-site communication using locally generated Global IDs.
>
>
> > Though an algorithm is suggested in 3.2.2. Perhaps SIXXS uses it. Anyway, the SIXXS tool seems pretty slick.
>
> One thing I'm not keen on that sixxs have done is to create a voluntary
> registry of the non-central ULAs. By creating a registry, I think some
> people who use it will then think that their ULA prefix is now
> guaranteed globally unique and is theirs forever. If there ever was a
> collision, those people are likely to point to that completely
> voluntary registry and say "I had it first" and are likely to refuse
> to accept that the voluntary registry has no status or authority over
> the random ULA address space.
Which is part one of the three things that have to happen to make ULA
really bad for the internet.

Part 2 will be when the first provider accepts a large sum of money to
route it within their public network between multiple sites owned by
the same customer.

Part 3 will be when that same provider (or some other provider in the
same boat) takes the next step and starts trading routes of ULA space
with other provider(s).

At that point, ULA = GUA without policy = very bad thing (tm).

Since feature creep of this form is kind of a given in internet history,
I have no reason to believe it won't happen eventually with ULA.

Owen