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 04:45 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 04:45:21 +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

> The math in RFC4193 for "uniqueness" considers *only a reduced number of 
uLA-based networks being inter-connected*. So, when computing global 
uniqueness, you should consider *all ULA prefixes in use*, not just 
those of networks you are interconnecting. And when you do that, you get 
a very high probability of collisions (~1).

This is getting unnecessarily complicated, IMO. ULAs are more than just link-local, because an administrative domain, such as even an enterprise net, can use them, throughout that network. Within such a domain, the top /48 can be guaranteed to be unique, because the same admin computes those 40 random Global ID bits. Not so? Such as, use the same PRNG, document the seed, then pick your five random bytes to use for each site, from the long random sequence.

Now you can organize that enterprise net into separate /48 networks, or for that matter, even link various geo-separated sites, through tunnels, where each site gets one or more of those random /48 prefixes. The important point being, only route inside that enterprise, and use a consistent method to compute the Global ID bits.

I just object to equating this with link-local. It's way more than that.