Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)

David Farmer <farmer@umn.edu> Sun, 14 February 2021 23:51 UTC

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From: David Farmer <farmer@umn.edu>
Date: Sun, 14 Feb 2021 17:51:18 -0600
Message-ID: <CAN-Dau3p4nGw=vz8h6rJAg62tnvusp+qn=soKiknNT_Y7_G0Uw@mail.gmail.com>
Subject: Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)
To: Ted Lemon <mellon@fugue.com>
Cc: "6man@ietf.org" <6man@ietf.org>, Brian E Carpenter <brian.e.carpenter@gmail.com>, Fernando Gont <fgont@si6networks.com>, Fred Baker <fredbaker.ietf@gmail.com>, IPv6 Operations <v6ops@ietf.org>
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On Sun, Feb 14, 2021 at 15:34 Ted Lemon <mellon@fugue.com> wrote:

> On Feb 14, 2021, at 4:14 PM, Fernando Gont <fgont@si6networks.com> wrote:
>
> That's not a legitimate use for GUAs.  Whereas in the case of ULAs, that
> the *intended* usage.
>
>
> Untrue. ULAs are intended to be globally unique. Your practical objections
> are correct, but have nothing to do with the architecturally defined scope
> of a ULA.
>

Ok, ULAs clearly belong in the Global Scope, we don’t want to use Zone
Indexes or Identifiers with them. Also, I agree that ULAs are “intended” to
be globally unique, and from all practical and architecture perspectives
they are, with two important caveats, both clearly stated in RFC4193, they
are not intended to be globally reachable and their uniqueness is
probabilistic.

Meaning there are no mathematical or procedural guarantees of uniqueness
for ULAs, especially across the entirety of the Internet. However, since
ULAs SHOULD NOT be globally reachable, from a practical and architectural
perspective, this detail, and inconvenient fact, is irrelevant.