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narenaryannarenaryan/agent-skills/skills/security/dnssec-sentinel-diagnostics/SKILL.md

dnssec-sentinel-diagnostics

Skill0 starsChanged 39 days agoMITView on GitHub

Use when checking DNSSEC root-key rollover readiness, interpreting root-key-sentinel SERVFAIL responses, or distinguishing an untrusted anchor from unsupported sentinel queries and resolver-path failures.

The file

We split this skill into the rules it gives an agent

2 rules. About 0 are common, 1 is distinctive, and 1 is very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈1

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 1

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Use A/AAAA, exact leftmost sentinel labels, five-digit decimal tags, and checking enabled (cd=false).

    line 14
  2. Distinctive:

    Check an ordinary signed control.

    line 18

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

DNSSEC Sentinel Diagnostics

A published DNSKEY is not evidence of a resolver's installed trust anchor. RFC 8509 deliberately turns one of two correctly signed sentinel answers into SERVFAIL. Interpret a controlled response pattern, never one successful lookup.

Establish the measurement path

Record resolver endpoint, transport, timestamp, target key tag, and controls. A browser's Secure DNS/VPN path may differ from the application's resolver. Query one explicit endpoint; even one anycast address can hide inconsistent backends.

Use A/AAAA, exact leftmost sentinel labels, five-digit decimal tags, and checking enabled (cd=false). Sentinel processing requires Secure validation. do=true requests DNSSEC records; it does not independently validate them.

Read the pattern

Check an ordinary signed control; require authenticated addresses for trust conclusions. Then evaluate these three queries together. Y means a matching address answer, not merely NOERROR; F means DNS SERVFAIL, not timeout/HTTP failure.

is-tanot-taBogus controlInterpretation
YFFConsistent with trusted target
FYFConsistent with untrusted target
YYFSentinel unsupported/indeterminate; anchor unknown
YYYValidation not demonstrated; anchor unknown
OtherInconclusive; investigate path/controls

Read-only example

Cloudflare-specific JSON DoH, with public test names:

for name in cloudflare.com dnssec-failed.org \
  root-key-sentinel-is-ta-38696.dnstest.dev \
  root-key-sentinel-not-ta-38696.dnstest.dev; do
  printf '\n%s\n' "$name"
  curl --fail --silent --show-error --max-time 15 \
    -H 'accept: application/dns-json' \
    "https://cloudflare-dns.com/dns-query?name=$name&type=A&cd=false"
done

Inspect DNS Status (0/2), address answers, and AD; HTTP 200 alone proves nothing. Repeat inconsistent results after relevant caches expire. Confirm missing trust through authorized operator inspection/vendor guidance before remediation; this recipe changes no settings.

Sources and validation

RFC 8509 §§2–4, Cloudflare's 2026-10-06 article, and IANA. On 2026-10-08, IANA lists 38696 for the scheduled October 11 rollover; recheck future tags/dates. Evidence and tests separate live observations from synthetic cases.

Pitfalls

  • Both sentinel answers succeeding does not establish readiness.
  • cd=true bypasses sentinel preconditions; never classify that response as readiness.
  • NXDOMAIN, empty NOERROR, failed controls, caching, and mixed forwarders invalidate simple conclusions.
  • DoH JSON is provider-specific; one path's snapshot does not certify another resolver or future rollover success.

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