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 mechanism 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 which actually responded is to have the name server include this information in the response itself. This note proposes a protocol extension to support this functionality.