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ECS Answer TTL (s)
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Categories: DNS , Networking , Security
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Introduction

You explore the Extension Mechanisms for DNS (EDNS) client-subnet option that adds an abbreviated IP prefix to requests. This information guides content-delivery networks toward region-specific servers, accelerating response times and improving locality-based routing.

The tester issues parallel DNS-over-HTTPS queries, one with client-subnet data and one without. Response sets appear side by side, letting you spot geo-adaptive answers, mismatched TTLs, or routing anomalies within milliseconds.

Validate records before launches, migrations, or cache-purge campaigns. Results rely on third-party resolvers whose behaviour may change without notice.

Technical Details:

The interface runs entirely in your browser on a lightweight reactive engine. It composes DNS-over-HTTPS requests, measures resolver latency with the Performance API, and renders results instantly. No query data is stored, logged, or sent to any server operated by this site.

Client Subnet Simulation

You define any IPv4/IPv6 prefix; the engine appends it to an EDNS0 option, emulating traffic from that location.

Dual-Path Comparison

A second request omits the subnet, revealing resolver defaults and enabling an at-a-glance difference check.

Real-Time Metrics

Query timers display round-trip latency badges so you can gauge resolver performance under variable network paths.

JSON Export & Clipboard

Copy or download the raw resolver response for audits, bug reports, or automated regression suites.

Visual Highlighting

Rows change colour when answer data diverges, directing attention to potential CDN or geolocation inconsistencies.

Step-by-Step Guide:

Follow these steps to replicate or compare DNS answers with precision.

  1. Enter a fully-qualified name in the Domain field (e.g. example.com).
  2. Select a Record Type such as A or MX from the dropdown.
  3. (Optional) Expand Advanced and adjust Client Subnet plus Prefix Length.
  4. Click to fetch answers with subnet data.
  5. Press to run a baseline query.
  6. Navigate between Answers and JSON tabs to review formatted or raw output.
  7. Use Copy JSON or Download JSON for external analysis.
  8. Repeat with different prefixes to assess global routing impact.

FAQ:

Need quick answers? Expand the topics below.

Is my data stored?

No. All look-ups execute locally; only the resolver you query sees the domain name and subnet prefix.

Which resolver is used?

The tester targets a public DNS-over-HTTPS endpoint at dns.google for consistent behaviour and CORS support.

Why do some answers differ?

Content-delivery networks optimise delivery by location; differing subnets may map to alternate IPs or CNAME chains.

Can I use IPv6 prefixes?

Yes. The prefix-length selector extends to 128 bits when an IPv6 address is detected in the subnet field.

Does TTL affect caching?

Absolutely. Low TTL values trigger frequent resolver refreshes, while higher values keep answers cached longer.

Troubleshooting:

Resolve common issues quickly.

  • “Domain required.” — Ensure the Domain field is not blank.
  • “Client IP required.” — Provide a subnet when testing A or AAAA records.
  • DoH error 403 — Check corporate firewalls or switch to an alternate resolver.
  • Unchanged answers — CDN may serve identical content worldwide; verify by altering prefix-length values.
  • Slow response times — Network congestion or resolver throttling can elevate latency; retry later or change networks.

Advanced Tips:

Get more from the tester.

  • Use /24 IPv4 and /56 IPv6 prefixes to approximate metro-area routing.
  • Run tests on different Wi-Fi and cellular networks to simulate ISP diversity.
  • Script automated fetches via DevTools > Console for overnight monitoring.
  • Combine JSON exports with diff tools to document CDN propagation stages.
  • Analyse TTL variance to refine cache-busting strategies during blue-green deployments.

Glossary:

Key terms you may encounter.

ECS
Option that transmits part of the client IP to DNS resolvers.
TTL
Time to Live; seconds an answer may be cached.
DoH
DNS-over-HTTPS; transports queries via HTTPS.
Prefix Length
Number of significant bits included in the subnet option.
CDN
Network that distributes content for faster delivery.
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