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

Ted Lemon <> Mon, 15 February 2021 13:37 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id D91F23A0A3B for <>; Mon, 15 Feb 2021 05:37:53 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: 0.001
X-Spam-Status: No, score=0.001 tagged_above=-999 required=5 tests=[DKIM_SIGNED=0.1, DKIM_VALID=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=unavailable autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id BvMwbp01789z for <>; Mon, 15 Feb 2021 05:37:49 -0800 (PST)
Received: from ( [IPv6:2607:f8b0:4864:20::f32]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 8C2323A09F6 for <>; Mon, 15 Feb 2021 05:37:49 -0800 (PST)
Received: by with SMTP id c25so3123518qvb.4 for <>; Mon, 15 Feb 2021 05:37:49 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20150623; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=1YLvUac763266V5jEMzEXCvfizm5osGommiBvr3fp2E=; b=mobyh6uR0sQuehHFuOD4c9ELF4WZUXzMPGIOyA5zLvF02qsqsvSN6lVO1aO+4CFkJi +46s/6ZGR8FoB56Ygotgb3tm+hGE1aUUQHIsDgQXlf12Vl7FeRz3xbpT5MX5FftUEak2 0vhkSsDT0EeuHwCIq41d9Lzo3H6jn9F/PRUBKHQWzGJWLbtm8ML14GTx6enrywdD9pjv 4v23vHDiV4ItXUdhlyc+AGUU1wjQp+ZRzz+PUPxDu46mETbKtwzyB13T47pu7uMTFPWq Oqaw/LjnpV9QhVmDWQbwHQPUNNBxgA27nr7pXrx2lS5IryG3GpQCM9MB0ic7EMacSVFp aTAA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=1YLvUac763266V5jEMzEXCvfizm5osGommiBvr3fp2E=; b=S8upNx9yqam3g9BTqP3Wisg+OLUF3Y7aMj12tpGmrpPjkbAFPwGbjQMrqkekLqrd2f GfFcTYXafljl9CDTHe56EFoMdBmZxUXG45REKexlBoip0CuzFVRyYPVrexTaLJiMDGby 5HB2X/c5GTGKm5LqLqSRphJomabDoHyY4aIFkf7YUv1lQW0L4EgzpYxBPI8URpowAxRY jSThUuzLWFKtEsi1vMSs/axBUYZICTXOSHrdSzRve0m6hGZDfYS9w0ktJs/OwDNI6g2P RGkUFXqK1aCkc7SYgoH4Tw0Y4rgKeYPuZRNI8UPMYVTSWMa6w95NhvaWc4BFlg6F5Od9 ioWw==
X-Gm-Message-State: AOAM530iKiMBO8qKrcO/PGP1+dGvSJu+/nPawkVCIhkUMh1fOpNm0z+S AMMA3NEbmJuPfky80XJaTjVsAQ==
X-Google-Smtp-Source: ABdhPJwY3ZD4zPc8mQex9mQcoYS5+A+35bUpquoydSHvvsSiKX9pbA78SXeYF1IWjN2lLmOzQe3VAg==
X-Received: by 2002:a0c:fb41:: with SMTP id b1mr13429859qvq.26.1613396268381; Mon, 15 Feb 2021 05:37:48 -0800 (PST)
Received: from ( []) by with ESMTPSA id y2sm5208544qkj.56.2021. (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 15 Feb 2021 05:37:47 -0800 (PST)
Content-Type: text/plain; charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.\))
From: Ted Lemon <>
In-Reply-To: <>
Date: Mon, 15 Feb 2021 08:37:45 -0500
Cc: "Manfredi (US), Albert E" <>, IPv6 Operations <>, "" <>
Content-Transfer-Encoding: quoted-printable
Message-Id: <>
References: <> <> <> <> <> <> <> <> <> <> <> <> <>
To: Fernando Gont <>
X-Mailer: Apple Mail (2.3654.
Archived-At: <>
Subject: Re: [v6ops] [EXTERNAL] Re: Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)
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: Mon, 15 Feb 2021 13:37:55 -0000

Fernando, I’m not going to retread this argument again. It’s clear that you and I disagree about what “global” means. You seem to want it to be some kind of guarantee, but it’s not. What’s also clear is that there isn’t any kind of consensus that there’s a problem here of the magnitude that you are suggesting. Your sole basis for saying that there’s a problem is that the definition of “global” in RFC 4007 doesn’t match the use of “global” in RFC 4193. I agree with you that this is the case, but this is not a problem statement that requires standards action. If someone is confused, you already know how to explain it to them.

I’m not going to participate in this discussion any further unless it becomes clear that the working group wants to take some action that will make things worse, in which case I will participate in the sense of opposing such action.

> On Feb 15, 2021, at 12:03 AM, Fernando Gont <> wrote:
> On 14/2/21 19:25, Manfredi (US), Albert E wrote:
>> -----Original Message-----
>> From: ipv6 <> On Behalf Of Fernando Gont
>>> ULAs can't be global.
>> I think we've been going around and around on this.
>> Maybe it's good to compare the ULA situation with RFC 1918 private IPv4 addresses. In such a comparison, it is clear that RFC 1918 addresses "can't be global," and must be used only within some admin domain. But it is also clear that the intention, or hope, of ULAs, is that they be globally unique.
> The intention is that, *given a subset of ULAs* the probability of collision is low.
>> Yes, in practice, we know that there is a non-zero probability that ULAs won’t be globally unique, but at the same time, it is false to claim that ULAs "can’t be" globally unique. 
> Please compute the birthday paradox assuming that each CPE in the world locally-generates a ULA prefix, and share the math with us. (that's what global scope means as per RFC4007)
> Spoiler: P~1
>> No one is telling us, "Go ahead and duplicate your ULAs, among admin domains, because they will be filtered out at border routers anyway."
>> At most, I'd add somewhere a notion of "only guaranteed within an administrative domain," and be done with it. I just don’t see how that is so confusing for anyone.
> As per RFC4007:
> scope means: topological span where the address is unique.
> global means: Internet-wide span
> Then we have this notion of "ULAs are 'global scope'", in which "global" meaning something different than what "global scope" means as per RFC4007. -- Hence the incongruence.
> e.g., if "global" means "an administrative domain", then that's not global -- unless you're also keen to argue that link-locals can be considered "global scope".
> Thanks,
> -- 
> Fernando Gont
> SI6 Networks
> e-mail:
> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
> _______________________________________________
> v6ops mailing list