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" <> Sun, 14 February 2021 22:26 UTC

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From: "Manfredi (US), Albert E" <>
To: Fernando Gont <>
CC: IPv6 Operations <>, "" <>
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)
Date: Sun, 14 Feb 2021 22:25:53 +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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-----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.

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. 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.