EDNS Client Subnet Lookup

Check if a DNS resolver supports EDNS Client Subnet (ECS). Enter a DNS server's IP address to see if it forwards client location data for faster CDN performance.

About EDNS Client Subnet (ECS)

EDNS Client Subnet is an extension to the DNS protocol that allows a recursive resolver (like a public DNS service) to include a portion of the user's IP address in the queries it sends to authoritative DNS servers.

How It Works & Why It Matters

Normally, an authoritative server only sees the IP address of the recursive resolver, not the end-user. If the user is in New York but the resolver is in California, a Content Delivery Network (CDN) might mistakenly serve content from a West Coast server, increasing latency.

By sending a part of the user's IP (e.g. `93.240.174.0/24`), ECS helps the CDN's DNS server provide a more accurate, geo-located response, directing the user to a nearby server for faster load times.

The Privacy Trade-Off

While ECS improves performance, it comes at the cost of privacy. Forwarding even a part of a user's IP address leaks information about their location to the authoritative DNS server and any networks in between. For this reason, many privacy-focused DNS services have this feature disabled.