Re: Why ULA: low collision chance (Was: IPv6 fc00::/7 — Unique local addresses)

Thu Oct 21 12:14:57 UTC 2010

That's assuming ULA would be the primary addressing scheme used.  If
that became the norm, I agree, the extra uniqueness would be
desirable, perhaps to the point that you should be asking an authority
for FC00::/8 space to be assigned.  But then why wouldn't you just ask
for a GUA at that point.  You could still randomly get "0", and if you
don't think people will keep cycling through random numbers until they
get something pretty you're underestimating human will to control
everything ;-)

I see ULA falling into the role of things like embedded device
management and sandbox networks, more than production, but who knows
what will become "the way" to engineer the IPv6 network of the next
decade.  We've only applied ULA to things like web-based network
registration and device management for devices that should never be
accessed from off the network (but even there, we've been more in the
mindset of using GUA with ACLs or null routes, etc to restrict
access).  It's really more of a utility address IMHO.

On Thu, Oct 21, 2010 at 7:47 AM, Jeroen Massar <jeroen at unfix.org> wrote:
> On 2010-10-21 13:33, Ray Soucy wrote:
> [..]
>> People may throw a fit at this, but as far as I'm concerned FD00::/8
>> will never leave the edge of our network (we null route ULA space
>> before it can leak out, just like you would with RFC1918 space).  So
>> you can pretty much use it has you see fit.  If you want to keep your
>> ULA space short there is nothing stopping you from using something
>> like FD00::1 as a valid address.
>
> And then your company gets bought and you need to merge networks, that
> is: renumber as they picked the same prefix.
>
> There is nothing wrong with RFC1918 per se, the big problem with it is
> that everybody else uses the same prefix, thus when you need to merge
> two networks you have collisions.
>
> I at one time also though that 'merging networks' and 'renumbering' is
> easy, till I heard stories from folks who where doing that for really
> large networks, who basically told that they where introducing 7+ layers
> of NAT to solve that issue, as renumbering is simply not doable if you
> have a global organization and if you are merging things like banks, for
> some magic reason they want to be able to talk to eachother.
>
> That is why there is ULA:
>  low chance of collisions if one wants to stay in the RFC1918 mindset.
>
> And if you want a guarantee of no collisions:
>  go to your favorite RIR and get a prefix from them.
>
> Greets,
>  Jeroen
>

-- 
Ray Soucy

Epic Communications Specialist

Phone: +1 (207) 561-3526

Networkmaine, a Unit of the University of Maine System
http://www.networkmaine.net/