Re: [IPv6] RFC 6724 shouldn't prefer partial reachability over reachability

Brian E Carpenter <> Sat, 25 November 2023 00:22 UTC

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Date: Sat, 25 Nov 2023 13:21:58 +1300
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To: Kyle Rose <>, Ed Horley <>
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From: Brian E Carpenter <>
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Subject: Re: [IPv6] RFC 6724 shouldn't prefer partial reachability over reachability
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On 25-Nov-23 13:11, Kyle Rose wrote:
> On Fri, Nov 24, 2023 at 5:49 PM Ed Horley < <>> wrote:
>     Other option is to just remove the ULA prefix entirely from 6724 and then the OS doesn’t see it as any different then GUA
> That won't work for any deployment that doesn't NAT/NPT ULA space (which is most of them) because without the label distinction a ULA source and GUA destination might be chosen, resulting in one of several obvious classes of unreachability in one direction or the other.
> ULA and GUA must be treated differently for purposes of address selection: what remains in dispute is exactly *how* that treatment should differ, not *whether* it should.

Yes. What we want, I think, is ULA->ULA to win over GUA->GUA and that means picking source and destination simultaneously. And we want ULA->GUA to never be tried unless the stack knows that NPTv6 is in place. And we can't do any of that correctly based on getaddrinfo() alone. So the draft is the best compromise given that we currently live with getaddrinfo().


> Kyle
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