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

Bob Hinden <> Tue, 16 February 2021 17:14 UTC

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From: Bob Hinden <>
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Date: Tue, 16 Feb 2021 09:14:08 -0800
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Cc: Bob Hinden <>, Ted Lemon <>, IPv6 Operations <>, "" <>
To: Fernando Gont <>
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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)
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> On Feb 15, 2021, at 8:05 PM, Fernando Gont <> wrote:
> On 16/2/21 00:16, Bob Hinden wrote:
>> Hi Ted,
>>> On Feb 15, 2021, at 2:05 PM, Ted Lemon <> wrote:
>>> On Feb 15, 2021, at 4:49 PM, Manfredi (US), Albert E <> wrote:
>>>> Your mention of birthday paradox depends on how many organizations use ULAs. If not many do, then the likelihood of global uniqueness goes up.
>>> There are also different uses for ULA. ULA can be used for internal addressing by large orgs, and there there’s potential for overlaps, if for no other reason than that large orgs sometimes merge.
>>> Another use for ULAs is on home networks. In this case, we don’t expect ULAs to ever need to cross the router. So the set of networks on which home network ULAs need to work is very tightly constrained, and we don’t need to worry about ambiguities.
>> As a datapoint for this, I own two home style routers from different vendors.   Both generate ULA prefixes automatically.   Vendors seem to have figured this out.
> FWIW, I don't think this issue has lead to interoperability problems. For the most part, the issue has to do with terminology/architecture, rather than whether things work in practice.

I am having a hard time seeing value updating a lot of specifications (even assuming we could agree about what to change) if there is not an interoperability problem.   What we have now appears to be adequate in-order to implement and use ULAs.

The whole reason for standards is to create interoperability.


> My hope was/is that terminology can be clarified in a way that folks reading the different addressing documents (RFC4291, RFC4193, RFC4007) don't find conflicting definitions or terminology.
> Some of this clarification might have a side-effect in things like programming-language macros and libraries, as e.g. has proven to be the case for Python.
> Thanks,
> --
> Fernando Gont
> SI6 Networks
> e-mail:
> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492