EDNS Client Subnet

Common card · No. 223919

EDNS Client Subnet (ECS) is an option in the Extension Mechanisms for DNS that allows a recursive DNS resolver to specify the subnetwork for the host or client on whose behalf it is making a DNS query. This is generally intended to help speed up the delivery of data from content delivery networks (CDNs), by allowing better use of DNS-based load balancing to select a service address near the client when the client computer is not necessarily near the recursive resolver. When an authoritative name server receives a DNS query, it takes advantage of ECS DNS extension to resolve the hostname to a CDN which is geolocated near to the client IP's subnet, hence the client makes further requests to a nearby CDN, thereby reducing latency. The EDNS client subnet mechanism is specified in RFC 7871.

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