[ISC-support #14369] Considering changing ECS caching strategy or negative data
Currently our ECS implementation caches all negative responses at the global scope.
A customer has requested that we store them at the learned scope.
RFC 7871 (Informational only) section 7.4, paragraph 4 notes that the original spec was ambiguous and hints that the interpretation of scoping negative answers is more likely to be used in future protocol specifications (if any) than caching them globally.
This issue is expected to be revisited in a future revision of the protocol, possibly blessing the mixing of positive and negative answers. There are implications for cache data structures that developers should consider when writing new ECS code.