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

Fred Baker <> Sat, 13 February 2021 01:52 UTC

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From: Fred Baker <>
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Date: Fri, 12 Feb 2021 17:51:55 -0800
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Cc: Fernando Gont <>,
To: Ted Lemon <>
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Subject: 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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> On Feb 12, 2021, at 4:53 PM, Ted Lemon <> wrote:
> But you think there’s a problem. In order for us to know what to do about this problem, you need to be able to articulate it in a way that makes sense to us. The best way to do so is to point to a case where the behavior of some system will be incorrect because this was not specified correctly. Can you point to such a case?

I think the thing Fernando is getting at would be the dictionary definition of "global", as in "anywhere on the globe". A ULA, as noted in the name, is a "local" address in the sense that it is only unique within a local context. It is "global" in scope only in the sense that if you get one from some other domain (which might legally happen if there were an agreement between the two AS's), the scope extends to include a domain other than the local one.

I commented that I think of it as a variant of site-local scope as defined in RFC 3513 in the sense that a site-local prefix was one assigned to a "site", whatever that actually was, and was only meaningful within that site. Should the packet cross into some other domain, the prefix would refer to the "site" of the domain it entered, which is a different "site" than the original. A ULA is similarly a prefix assigned to a local routing domain, and addresses within it are only meaningful or useful within that routing domain. If there is a difference, it is that (a) when it crosses a domain boundary, the new domain might not actually contain that prefix, unless the routing domain were be extended across ASN boundaries by prior arrangement. So it's not *exactly* the same as a site-local, but it bears (at least to my dense mind) strong similarities.

I made the observation because I'm watching several people struggle with the idea that something is global in "scope" but not globally understood. I view that as a poor definition of the scope. If we're trying to identify the scope, it has to be something meaningful. We shouldn't have to struggle with it.