Re: [v6ops] Implementation Status of PREF64

Owen DeLong <> Wed, 13 October 2021 17:50 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id ABBC03A08AC; Wed, 13 Oct 2021 10:50:39 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.099
X-Spam-Status: No, score=-2.099 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (1024-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id BlyTX93BO-GE; Wed, 13 Oct 2021 10:50:35 -0700 (PDT)
Received: from ( [IPv6:2620:0:930::200:2]) by (Postfix) with ESMTP id BC1893A0890; Wed, 13 Oct 2021 10:50:34 -0700 (PDT)
Received: from ([IPv6:2620:0:930:0:14af:8646:5244:2bdd]) (authenticated bits=0) by (8.16.1/8.15.2) with ESMTPSA id 19DHoY6h3976826 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 13 Oct 2021 10:50:34 -0700
DKIM-Filter: OpenDKIM Filter v2.11.0 19DHoY6h3976826
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=mail; t=1634147434; bh=G/M0mK+pehKgNPnveiGs787OWNWQt6+yirp+yLh2xi0=; h=Subject:From:In-Reply-To:Date:Cc:References:To:From; b=4ZIlWUX/YlEV1JDNvyaiUqDMVcIb96TzkEYQ9kSHuTrdfHNUw//65XpmyK0cGI6pW dvao+VfRasuhze7a7zBgiSrop5O+nVpExr8UH7SQEKWuEY21w2GrOLKg0h5xxSeXxX 5y/BeGpxvIIAqdSKK+9g1/PMOC0RIkgfhn1bNBFc=
Content-Type: text/plain; charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.\))
From: Owen DeLong <>
In-Reply-To: <YWcYmfTdw40rR4r7@Space.Net>
Date: Wed, 13 Oct 2021 10:50:33 -0700
Cc: "Pascal Thubert (pthubert)" <>, v6ops list <>, Lorenzo Colitti <>
Content-Transfer-Encoding: quoted-printable
Message-Id: <>
References: <> <> <> <> <> <> <YWW1ghmjueHmfCEb@Space.Net> <> <YWcPm49GzkJZDYTP@Space.Net> <> <YWcYmfTdw40rR4r7@Space.Net>
To: Gert Doering <>
X-Mailer: Apple Mail (2.3654.
X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.6.4 ( [IPv6:2620:0:930:0:0:0:200:2]); Wed, 13 Oct 2021 10:50:34 -0700 (PDT)
Archived-At: <>
Subject: Re: [v6ops] Implementation Status of PREF64
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: v6ops discussion list <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Wed, 13 Oct 2021 17:50:40 -0000

> On Oct 13, 2021, at 10:34 , Gert Doering <> wrote:
> Hi,
> On Wed, Oct 13, 2021 at 10:23:28AM -0700, Owen DeLong wrote:
>>> Thinking we have arbitrary number of /64s to burn will have a hard landing
>>> when reality comes along.
>> Will it? Here???s reality???
>> More than enough /48s in 2000::/3 (1/8th of the total space) to hand out a few
>> hundred to every building now in existence or likely to ever exist.
> You're overlooking intermediate hierarchies, and loss involved with that.

Nope… Not really…

Let’s divide ISPs into three categories — Small-ish, under 1M subscribers,
probably well served by a /28. Large (between 1M and 5M subscribers,
probably need a /24), and Huge — The Comcast/Verizon/etc. of the world,
who likely need a /12.

I’ll assert that there are probably 2-5 million, so let’s call it 5 million ISPs in the
small-ish category, a million or so in the large category, and maybe 200 world-
wide in the Huge category.

So that’s 5M /28s + 1M /24s + 200 /12s.

5M rounded up to a nibble boundary works out to 24 bits (16.7M), so 
subtracting from a /28, that gets us to a /4 which is 1/2 of 2000::/3.

Issuing a million (20 bits) /24s is another /4, so we’ve burned the other
half of 2000::/3.

Now we need to cover 200 /12s, which we can do from 4000::/3 and
still have 312 /12s to deal with any additional needs that may arise
and even if we burn through all of that, we’ve only used 25% of the
total address space.

> Can it be made to work?  Of course.


> Can we have another quintillion for everybody's k8s clusters, and another
> one for every desktop PC with VMs on it?  Of course.

Quintillion addresses? Sure, 18 per. That’s a /64.

However, unless you expect an average building to exceed 50,000 such
combinations of devices, that still aggregates to a /48 for the building.

> Will we wake up to see that the start of this plan wasn't the best of ideas?

I doubt it. So far, the math seems to work.

> So, no, assigning whole /64s to large-numbered device types (unless they 
> serve as routers for one or more subnets, in which case I *do* support 
> delegating at least one standard-subnet-size per subnet) is not something
> I think we should do.  Balance needs to be found.

I think so far, there’s no evidence to suggest that /64 is not a good balance point.

The devices in question are, effectively routers, so it seems we agree.