EDNS Client Subnet (ECS) Checker
Test if recursive DNS resolvers support and forward EDNS Client Subnet (ECS) OPT pseudosection metadata (RFC 7871) to authoritative nameservers for geo-steering routing.
Evaluating Resolver EDNS support...
Checking if client subnet records are forwarded intact to authoritative servers.
Subnet Verification
EDNS0 Option Payload Details
What Is EDNS Client Subnet (ECS / RFC 7871)?
EDNS Client Subnet (ECS) (RFC 7871) is an extension to the DNS protocol (EDNS0 / RFC 6891) that allows recursive DNS resolvers (such as Google Public DNS 8.8.8.8) to pass a truncated portion of the requesting client's IP address (typically a /24 prefix) to authoritative nameservers.
Why ECS Is Critical for Content Delivery Networks (CDNs)
Without ECS, authoritative DNS servers for CDNs (Cloudflare, Akamai, AWS CloudFront) only see the IP address of the recursive resolver, not the end user. With ECS enabled, CDNs return the nearest edge node server IP address relative to the client's actual geographic location, reducing web latency.
Privacy Considerations
To preserve user privacy, ECS never transmits full IP addresses; it truncates IPv4 addresses to /24 (256 IP block) and IPv6 addresses to /56 or /64 prefixes.