Captures the v3 design: IPAddressDeny= alone (no IPAddressAllow=any
because the documented "more specific wins" semantics don't hold on
systemd 257 / kernel 6.12 — the allow trumps unconditionally), explicit
CIDRs (the -p parser rejects the localhost/link-local shorthand
keywords), and a static sandbox-only resolv.conf bind to keep DNS
reachable when private RFC1918 ranges are blocked.
Plan documents what was implemented (in 7e66936) and the lessons
surfaced during execution so the next person doesn't have to rediscover
them.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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