R8 research: both in-repo citations fail; charm default is IPv6; new MTU risk found ...

Operator declined to rule on the overlay's own citations -- "I would like
documentation and vendor specific information rather than conjecture. Research is
cheap, guesswork is expensive" -- then directed a full read of two bugs weighed
against current versions. That was the right call and it inverted the answer.

BOTH CITATIONS IN overlays/dc-dc-ipv6-family-matrix.yaml FAIL ON INSPECTION:
- LP #1913409 is Fix Released (2021) against kolla-ansible, a DIFFERENT
  INSTALLER. No bearing on a Juju/charm deployment.
- LP #1911788 is Incomplete and a DUPLICATE of LP #1896630, and is NOT an IPv6
  defect. Its diagnosed cause is an OVN port-binding hostname mismatch --
  binding_host_id carrying the shortname instead of the FQDN for LXD containers
  on MAAS, giving binding_failed instead of ovs. The IPv6 address in the timeout
  was incidental; the port never bound, so nothing would have worked over any
  family.

VERSION WEIGHING, verified rather than asserted. #1896630's primary fix is
ovs-record-hostname.service, which the bug places in OVS 2.15 (Focal shipped
2.13). Rather than assume, I queried THIS DEPLOYMENT'S OWN dc0 mirror for what a
jammy node would actually install: openvswitch-switch 2.17.0-0ubuntu1 (jammy) and
2.17.9-0ubuntu0.22.04.2 (jammy-updates). 2.17.9 >> 2.15, so the fix is present on
every node this deployment will build. The bug's era was Juju 2.7.8, charms 20.08
Ussuri, Focal/OVS 2.13; we are Juju 3.6.27, charms 2024.1, jammy/OVS 2.17.9. The
charm-layer-ovn task -- the one closest to this repo's OVN usage -- is closed
Invalid.

AND THE DEFAULT RUNS THE OTHER WAY: LP #1897418 records, verbatim, "By default,
Octavia charm uses ipv6 for its lb-mgmt-subnet", with a reporter noting success
"using the charm default (ipv6) network but using ipv4 everywhere else". Upstream
Octavia documents that "IPv6 subnets can be used for the LB Network". So D-101's
IPv6-only placement of lb-mgmt is ALIGNED with the charm default, and a v4-only
lb-mgmt-net would be the DEPARTURE requiring justification -- the opposite of how
R8 was first framed.

NEW LIVE RISK FOUND, COUPLED TO THE R3 RULING: LP #2018998 "MTU mismatch between
o-hm0 and lb-mgmt-net" (charm-octavia, High, Edward Hope-Morley). A jumbo
lb-mgmt-net beside a 1500 o-hm0 silently drops health messages over 1500 bytes
and triggers SPURIOUS load-balancer failovers -- evidenced in the bug as "UDP,
length 1534 > 1500 and o-hm0 never receives them" and "o-hm0: dropped over-mtu
packet: 1744 > 1500". Fix Released across our lineage, BUT a recurrence was
reported 2025-12-31 against octavia 14.0.0 / 2024.1 stable, the exact channel
bundle.yaml pins. R3 ruled the underlay be finished to jumbo, which is precisely
this bug's precondition. OWED at the Octavia step of Stage 5: verify o-hm0's MTU
MATCHES lb-mgmt-net's after deploy, not merely that the charm claims to set it.

GENERALISABLE LESSON, recorded in the capture: a bug NUMBER in a comment is an
existence claim; what the bug SAYS is the content, and only content is evidence.
Same class as the two ruled-but-never-built decisions this audit already found --
a plausible in-repo statement that nothing verifies.

R8 is NOT ruled by this commit. It will be re-presented on corrected evidence.

Revert: git revert this commit; the capture is new and CURRENT-STATE additive.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HvCyrwvYTTcDYnRErfMsNf