Re: [v6ops] I-D Action: draft-gont-v6ops-ipv6-addressing-considerations-00.txt

Brian E Carpenter <> Thu, 31 December 2020 19:47 UTC

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To: Gert Doering <>
Cc: Fernando Gont <>, IPv6 Operations <>,
References: <> <> <> <> <> <> <20201231103010.GL13005@Space.Net>
From: Brian E Carpenter <>
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Date: Fri, 1 Jan 2021 08:47:31 +1300
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Subject: Re: [v6ops] I-D Action: draft-gont-v6ops-ipv6-addressing-considerations-00.txt
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On 31-Dec-20 23:30, Gert Doering wrote:
> Hi,
> On Thu, Dec 31, 2020 at 02:00:33PM +1300, Brian E Carpenter wrote:
>> 4. The following table attempts to show some of the distinctions
>> involved (simplified). View in a fixed-width font. You may not
>> agree with it...
>> Unicast       Prefix      IID        Routeable   Announced
>> address       assigned    assigned
>> types         by          by
>> -----------------------------------------------------------
>> Link-local    fixed       host       no          no
>>               by RFC
>> ULA           user/RA     host or    yes         IGP only
>>               (random)    DHCPv6
>> GUA           IANA/RIR/   host or    yes         IGP,
>>               ISP/user/RA DHCPv6                 BGP4 by policy
> Indeed, I am not agreeing - as there is nothing that prevents ULAs from 
> being transported by BGP.

Indeed, nothing in the laws of physics, but it's default-forbidden by
an RFC ;-). Exactly how to express that in a short table is tricky.

I think we all agree about this; what Fernando's draft shows is that it
is quite hard to describe, and the word "global" is confusing.
(Really for the same reason that URLs were renamed from "universal"
to "uniform" in 1994. But renaming "global" at this stage seems almost


> We use ULAs for "services that must never reachable from the Internet",
> and our routing being what it is, everything is transported by BGP - only
> loopbacks in OSPF.  The difference is "do we announce it to other ASes?"
> So maybe this should be "generally expected to be visible by other
> networks on the Internet" (ULA: no, GUA: yes).
> But that's neither precise nor does "expected" mandate anything - I might
> want to announce our ULA prefix to our sister company, using eBGP, and
> I might decide to not announce our GUA IPv6 PI /48 that we use for our
> backbone infra "because people are not supposed to send packets there"...
> Gert Doering
>         -- NetMaster