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

Michael Richardson <> Sun, 26 November 2023 18:07 UTC

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From: Michael Richardson <>
To: Kyle Rose <>, 6man WG <>
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References: <> <> <> <> <> <> <> <> <> <> <> <458732.1701012011@dyas> <>
Comments: In-reply-to Kyle Rose <> message dated "Sun, 26 Nov 2023 10:59:14 -0500."
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Date: Sun, 26 Nov 2023 19:07:41 +0100
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Subject: Re: [IPv6] RFC 6724 shouldn't prefer partial reachability over reachability
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Kyle Rose <> wrote:
    >> But, you as an operator, would be deleting those announcements based
    >> upon your well configured BCP38.  So, it's really is entirely under
    >> your control, which I agree with you: is a better.

    > I am not referring to leaking routes, but to leaking rendezvous
    > information, i.e., DNS. In a world in which operators run recursive

Ah, thank you for the clarification!

    > resolvers that clients can be assumed to use when on your network, you
    > maybe can configure yours to drop all external address records
    > referring to ULA or 1918 space, but we're now in a world in which
    > privacy (via DoH/DoQ) and end-to-end integrity (via DNSSEC) have been
    > prioritized over operability, so you have to assume you won't have full
    > control over what DNS entries a client sees. This has implications for
    > the set of trade-offs involved in misconfigurations, especially when
    > the naive user blames you for something not working even when it's
    > mostly not under your control.

I completely agree, and it's one reason why I think split-horizon DNS is a
failed experiment.  Please use, and I really wish more
people would ask the ADD WG to make that the primary suggestion going
forward.  (The IETF has never before defined what split-horizon DNS is. It
goes back to Cheswick&Bellovin's _Firewalls_ book of ~1990, and perhaps before)

    > With border routers sending ICMP
    > unreachable rejections, working Happy Eyeballs would hopefully make
    > failover transparent, but "hopefully" is doing a lot of heavy lifting
    > in that expectation.

I think that HE is a very specific mechanism :-)
Trying all addresses and having ICMPs ought to be enough, even if it might be slower.

    > Anyway, I consider this an acceptable set of trade-offs, but there is a
    > discussion to be had about the implications that would benefit from the
    > experience of big-time operators who have run into a much broader set
    > of issues than I have.

We are in agreement here then.

Michael Richardson <>, Sandelman Software Works
 -= IPv6 IoT consulting =-                      *I*LIKE*TRAINS*