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

"Manfredi (US), Albert E" <> Wed, 06 January 2021 05:54 UTC

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From: "Manfredi (US), Albert E" <>
To: Fernando Gont <>
CC: IPv6 Operations <>, 6MAN <>
Thread-Topic: [EXTERNAL] Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)
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Date: Wed, 6 Jan 2021 05:53:45 +0000
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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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Hi Fernando, let's follow the KISS principle.

-----Original Message-----
From: Fernando Gont <> 

> RFC4193 does not mandate a specific algorithm, but rather specified the 
requirements for the PRNG (good for the RFC4193 authors!). So, 
documenting the seed will serve no purpose, because other 
implementations might use a completely different algorithm for 
generating the ULA prefix.

Within an enterprise, the admin has a choice of which PRNG to use, and what seed to use. Think in terms of one guy, making that decision, and then documenting all the Global ID 40-bit sequences in use, in the various nets of the enterprise. The guy with this responsibility can certainly decide on which algorithm to use!

It is easy enough to guarantee uniqueness, in this case.

> An this one is obviously non-enforceable, for multiple reasons, 
including the fact that RFC4193 doesn't mandate any specific algorithm.

I am the enterprise admin, I'm tasked with administering the ULAs for the enterprise, and I enforce the rule. The admin of one enterprise network has no say in what other admins, of other enterprise networks, want to do. Nor is there any requirement for ULAs of different enterprise nets to be mutually unique.

> I don't think anybody has equated ULAs with link-locals. The argument 
has been, instead, that: scope(link-local) < scope(ULA) < scope(GUA)

Something like "single administrative domain scope," if that existed, makes sense to me. I think the problem is that today, it's either link local or global scope?

> In a way, the expectation of ULAs to be global-scope is probably what 
drove the recent discussion on the 6man list about a ULA registry --

To me, that's a different discussion. That registry idea would probably be a necessity, but only for the fc00::/8 ULAs, which are for future use. When ULAs are not assigned by an individual admin, the problem of uniqueness is different, no? To me, that registry problem is a non-issue, unless and until we start using the fc00::/8 addresses. As of now, only fd00::/8 are being discussed.