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

Fernando Gont <> Tue, 16 February 2021 04:05 UTC

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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)
To: Bob Hinden <>, Ted Lemon <>
Cc: "Manfredi (US), Albert E" <>, IPv6 Operations <>, "" <>
References: <> <> <> <> <> <> <> <> <> <> <> <> <> <> <> <>
From: Fernando Gont <>
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Date: Tue, 16 Feb 2021 01:05:05 -0300
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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.

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.

Fernando Gont
SI6 Networks
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492