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Glossary

Review definitions for Cloudflare Zero Trust terms.

TermDefinition
EDNS Client Subnet (ECS)

ECS is a DNS extension that enables recursive DNS resolvers to include client IP address information in their DNS queries.

Not all resolvers use ECS but, if they do, usually a part of the IP address is omitted. Sending ECS headers is generally intended to reduce latency and speed up content delivery in connection to CDNs and load balancers. The ECS mechanism is specified in RFC 7871.