EDNS Client Subnet, referred to as ECS, affects how UltraDNS provides directional responses. Enabling ECS improves accuracy based on the end user’s location, while disabling it can reduce DNS query volume and associated billing.
What ECS Is
EDNS Client Subnet is an extension of DNS that allows recursive DNS servers to include a portion of the client’s IP address in DNS queries sent to authoritative DNS providers.
Without ECS, UltraDNS only sees the IP address of the recursive DNS resolver. With ECS enabled, UltraDNS can also use the client’s IP information to provide more location-aware responses.
How ECS Affects DNS Responses
When ECS is enabled, directional DNS responses are based on the client’s location rather than the location of the recursive DNS resolver.
For example, if a user is located in Arizona but uses a recursive DNS resolver in Colorado, ECS allows UltraDNS to return a response based on Arizona. Without ECS, the response would be based on Colorado.
Impact on Query Volume and Caching
ECS affects how DNS responses are cached by recursive resolvers.
Without ECS, a recursive resolver can cache a single response and reuse it for many users. With ECS enabled, responses may vary based on client IP ranges, which results in multiple cached entries instead of one.
This reduces cache efficiency and increases the number of queries sent to UltraDNS, which can lead to higher query volume and billing.
When to Enable or Disable ECS
Enabling ECS improves the accuracy and stability of directional DNS answers, particularly for users of public recursive resolvers such as Google Public DNS and OpenDNS.
Disabling ECS can reduce overall query volume by allowing recursive resolvers to cache and reuse responses more effectively.
The decision to enable or disable ECS depends on whether accuracy of geographic or directional responses is more important than minimizing query volume.