Extended DNS (EDNS) lets queries carry extra data. The Client Subnet option (ECS) discloses the requester’s network prefix, allowing authoritative servers to steer traffic toward optimal endpoints across the internet.
The EDNS Client-Subnet Tester sends DNS-over-HTTPS queries to Google Public DNS and shows how responses change when you alter the subnet. Enter a domain, record type, subnet, and prefix; the tool returns each answer with its TTL for immediate comparison.
Use the results to verify geo-routing, evaluate anycast builds, or confirm security boundaries before deployment. All processing occurs in-browser, so you examine live behaviour without exposing infrastructure secrets or relying on external services.
Technical Details:
The tester performs live look-ups and renders results in real time.
- Queries the DNS-over-HTTPS endpoint
dns.google. - Adds
edns_client_subnetto every request. - Accepts A, AAAA, MX, NS, TXT, and CNAME records.
- Parses JSON
Answerarrays and strips quotes. - Validates domain, IP, and prefix length in-browser.
- Times each request with the high-resolution Performance API.
- Stores no data server-side; only the DoH call leaves your browser.
https://dns.google/resolve?name=example.com&type=A&edns_client_subnet=1.2.3.0/24Step-by-Step Guide:
Follow these steps to compare answers across subnets.
- Open the tool and focus on the Domain field.
- Type the fully qualified domain name you wish to test.
- Select the desired record type from the drop-down menu.
- Enter a client IP prefix such as
1.2.3.0. - Set the prefix length in bits; Tip /24 suits most IPv4 tests.
- Click Test ECS to send the query.
- Review the answer list and TTL values displayed below.
- Adjust the subnet or record type and repeat as needed.
FAQ:
The answers below address common questions.
Why use Google Public DNS instead of my resolver?
Google’s DoH service is globally anycast and honours ECS, providing consistent, low-latency testing from anywhere.
Does the tool change my DNS records?
No. It performs read-only queries and never modifies authoritative data.
Is my query history stored?
Nothing is logged in your browser or on the site; only Google Public DNS sees the request.
How accurate is the response time metric?
The value is measured with performance.now() and includes network latency plus DoH processing.
Can I automate bulk testing?
Yes. Capture generated URLs and run them with your own scripting to gather large datasets.
No data is transmitted or stored server-side.