Re: Non routable IPv6 registry proposal

[David Farmer <[e-mail]>]

On Thu, Mar 11, 2021 at 2:16 PM Brian E Carpenter <
[e-mail]> wrote:

> David,
> On 12-Mar-21 08:19, David Farmer wrote:
> > On Thu, Mar 11, 2021 at 10:49 AM Keith Moore <[e-mail]
> <mailto:[e-mail]>> wrote:
> >
> >     On 3/11/21 5:22 AM, Nico Schottelius wrote:
> >
> >>>     Another question I have is whether such ULA allocations
> >>>     will realistically remain local.
> >>     ULAs are unlikely staying local, as we have seen with radio
> networks in
> >>     Germany. Tunnels are being used to interconnect remote cities and
> >>     non-collision (not necessarily public routing) are a primary
> concern.
> >
> >     Despite the name, there's no reason that ULAs should stay local.
> As long as they are properly chosen, it's perfectly reasonable to route
> them privately between cooperating networks, and IMO this is part of their
> design.   One of the problems with RFC 1918 addresses in IPv4 was that
> enterprises had a need to route traffic between networks each using that
> space.   The resulting address collisions generally required explicit NAT
> configurations to work around, and these were failure-prone and difficult
> to manage.  ULAs were intended in part to remedy this problem.
> >
> >     Keith
> >
> > The "L" for Local isn't intended to have a strict definition of Local.
> However, similarly, the "U" for Unique isn't intended to have a strict
> definition of Unique either, especially a mathematical definition of
> Unique.
> >
> > You can easily interconnect thousands or even tens of thousands of ULA
> prefixes without much chance of an address collision, as long as the random
> assignment process is actually used. Whereas, if you try to interconnect
> billions of ULA prefixes, you will probably start running into the birthday
> paradox.
> >
> > So the interconnection of ULA prefixes, the route-ability of them, is
> not intended to be unlimited. There are limits to the number of ULA
> prefixes that SHOULD be interconnected to each other; nevertheless, this
> limit is extremely generous for the intended use cases.
> >
> > If you disregard the intended use cases and use them outside the
> intended use cases, then address collisions could become an issue.
>
> I'm not sure where you get your "intended" from. I don't think we've ever
> really written done the intended use cases in such detail. (Except for the
> abandoned
> https://datatracker.ietf.org/doc/html/draft-ietf-v6ops-ula-usage-considerations-02
> )
>
>     Brian
>

The first sentence of the Abstract for RFC4193 says;


This document defines an IPv6 unicast address format that is globally
unique and is intended for local communications, usually inside of a site.


This is expanded upon in the first paragraph of the Introduction to RFC4193;

This document defines an IPv6 unicast address format that is
globally unique and is intended for local communications [IPV6]. ...
They are routable inside of a more limited area such as a site.  They may
also be routed between a limited set of sites.


Those sound a lot like intended use cases to me, the key phrases in that
for me are, "local communications", "usually ... a site", and "a limited
set of sites."

Yes, that's pretty vague, but I don't see a reasonable interpretation of
those phrases that include every site on the Internet, or even every site
in a country or state, maybe it could include every site in a small to
modest city, but even that's a bit of a stretch in my opinion.

YMMV
Thanks

-- 
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