SkillVaultskills Browse all 500 skills

Networking · Version 1.3.0 · Reviewed 2026-08-02

DNS Troubleshooter

Make a defensible decision about record and delegation checks and propagation diagnosis with evidence, explicit trade-offs, and a verification plan.

4 method steps 5 documented failure modes 4 diagnostic checks 7 quality gates

Explains resolution failures across authoritative records, recursive resolvers, negative caching, delegation, split-horizon DNS, and stale TTL behavior.

₹99 one-time

Get this skill archive

What this skill helps you do

  • Record and delegation checks
  • Propagation diagnosis
  • Split-horizon debugging

How DNS Troubleshooter works

You provide

Failing request path, timings, and intermediary configuration

It inspects

Layer isolation for record and delegation checks: resolve, connect, handshake

It decides

A propagation diagnosis fix attributed to a specific hop

You verify

Reproduce from the affected path, not from a healthy one

What it checks first

DNS Troubleshooter explains resolution failures across authoritative records, recursive resolvers, negative caching, delegation, split-horizon DNS, and stale TTL behavior. Use it when the work involves Record and delegation checks, Propagation diagnosis, Split-horizon debugging.

  1. Which layer the failure occurs at, since a name-resolution failure and a TLS failure look similar to the application.
  2. Whether the failure is symmetric, because one-way reachability points at policy rather than transport.
  3. Timing: connection setup, first byte, and transfer are separate problems with separate causes.
  4. Whether intermediaries such as proxies, load balancers, or service meshes terminate the connection.

Failure modes it recognizes

  • DNS search-path expansion adding latency and intermittent failures for external names.
  • An idle timeout on an intermediary silently closing connections a pool still believes are open.
  • MTU mismatch causing large payloads to hang while small requests succeed.
  • TLS SNI or certificate mismatch surfacing as a connection reset with no application log.
  • A policy denying return traffic, producing a timeout rather than a refusal.

Answers it will reject

  • Blaming the network before confirming resolution, routing, and policy each independently.
  • Increasing timeouts to mask an intermediary that is closing connections deliberately.
  • Testing from a different host or network than the one experiencing the failure.

Decision rules it applies

  • Isolate the layer before proposing a fix: resolve, connect, handshake, then request.
  • Reproduce from the affected network path; a successful test from elsewhere proves nothing.
  • Prefer connection-level evidence over application logs when the failure is pre-response.

Evidence it asks for

  • Capture resolution, connect, TLS, and first-byte timings separately.
  • Test with and without the intermediary to attribute the reset.
  • Confirm reachability in both directions rather than assuming symmetry.

The method inside

  1. Establish what is actually true about record and delegation checks from the supplied evidence, and mark what is missing.
  2. Identify the mechanism behind propagation diagnosis rather than restating the symptom.
  3. Choose the smallest defensible change for split-horizon debugging, weighing impact, confidence, effort, and reversibility.
  4. Record consequences, rollback, and open questions

Deliverables

  • Record and delegation checks assessment
  • Propagation diagnosis decision and action plan
  • Split-horizon debugging verification checklist

Evidence requirements

  • Functional and quality requirements
  • Scale, latency, consistency, cost, and compliance constraints
  • Current topology and alternatives considered

Quality gates

  • Every material claim traces to supplied evidence or is labeled as a hypothesis.
  • The response follows the declared deliverable contract.
  • No execution, access, measurement, or verification is invented.
  • Secrets and personal data are redacted rather than repeated.
  • The user receives a concrete independent verification step.
  • The relevant failure modes in this domain were considered rather than only the reported symptom.
  • No listed anti-pattern was recommended as a solution.

Example task

Input

The new API hostname resolves correctly from my laptop but returns NXDOMAIN from our Kubernetes cluster.

Expected output

The cluster resolver is caching the earlier negative answer. The SOA negative TTL is 900 seconds, which explains why public resolvers already see the record while CoreDNS still returns NXDOMAIN...

Boundaries and compatibility

Ideal for

  • Record and delegation checks: produce a decision or artifact grounded in supplied evidence.
  • Propagation diagnosis: produce a decision or artifact grounded in supplied evidence.
  • Split-horizon debugging: produce a decision or artifact grounded in supplied evidence.

Out of scope

  • Producing a generic reference architecture without requirements
  • Hiding material trade-offs behind best-practice language

Agent compatibility

  • GitHub Copilot custom agents
  • Claude Agent Skills / SKILL.md
  • Any instruction-following chat model

Tool policy: Advisory by default. No tools are assumed. If the host provides tools, use read-only evidence gathering unless the user explicitly approves a scoped write or execution action.