Introduction - If you have any usage issues, please Google them yourself
Abstract
With the increased use of DNS anycast, load balancing, and other
mechanisms allowing more than one DNS name server to share a single
IP address, it is sometimes difficult to tell which of a pool of name
servers has answered a particular query. While existing ad-hoc
mechanisms allow an operator to send follow-up queries when it is
necessary to debug such a configuration, the only completely reliable
way to obtain the identity of the name server that responded is to
have the name server include this information in the response itself.
This note defines a protocol extension to support this functionality.