Re: [IPv6] I-D Action: draft-ietf-6man-rfc6724-update-04.txt

Kyle Rose <> Mon, 27 November 2023 15:58 UTC

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From: Kyle Rose <>
Date: Mon, 27 Nov 2023 10:58:36 -0500
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To: Timothy Winters <>
Cc: Mark Smith <>, Tim Chown <>, 6man Chairs <>, 6man WG <>
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Subject: Re: [IPv6] I-D Action: draft-ietf-6man-rfc6724-update-04.txt
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I never got around to responding to Mark, so thanks for reminding me.
Because I strongly disagree with this:

> If it's going to put ULAs below GUAs, then both RFC 4193 (ULA RFC) and
>> RFC 7084 (IPv6 CE (CPE) RFC) need to be updated by this draft. I don't
>> agree with that preference of ULA below GUAs, however if that is going
>> to be the WG's consensus, then the consequences are greater than just
>> an update to RFC 6724.
>> RFC 4193:
>> The following advice and use cases need to be updated/negated/removed,
>> as if a local network's hosts have both GUA and ULA addresses, and
>> they're provided to a local network host via DNS, such as via
>> multicast DNS in RFC 7084, then the ULA addresses will never be used,
>> because the GUA addresses are preferred, making renumbering GUA
>> prefixes impossible without disrupting local network communications.
>> Consequently, it would be best if ULA addressing wasn't be deployed if
>> a network has GUA addressing, or ULA addressing should be deprecated
>> when GUA addressing is deployed, with the benefit being saving on
>> router and host processing of an address space that is unlikely to
>> ever be used.
> ...

> ULA requirements:
>> ULA-6:
>> "A CE SHOULD deprecate any ULA prefixes it is announcing when it
>> commences providing GUA addressing to hosts, by announcing its ULA
>> prefixes with a Preferred Lifetime of zero seconds, and a decrementing
>> Valid Lifetime, and then cease announcing its ULA prefixes when the
>> Valid Lifetime reaches zero seconds.
>> Should a GUA address space become unavailable, the CE's ULA address
>> space again be announced with the CE's ULA appropriate Preferred and
>> Valid Lifetimes."
I deploy multi-prefix, one provider-delegated GUA and one ULA, to all of my
v6 clients via RA. I specifically don't have any hostnames with both ULA
and GUA AAAA records to avoid the problem Mark is pointing out: internal
services are on their own subdomain that maps exclusively to ULA and 1918
addresses. I *want* both address schemes simultaneously in parallel,
specifically so I can avoid the need to change DNS entries when my provider
decides I've had a PD for too long and capriciously changes it. This scheme
has been working great for me for 5 years, in part because the Debian
gai.conf doesn't comply with 3484 or 6724 and (correctly, IMO) prefers ULA
to IPv4. (Someone "fixed the glitch".)