Acknowledgments

The main idea in this document is taken from [DNSRRR], Section 3, "Stopping Downward Cache Search on NXDOMAIN". Thanks to its authors, Paul Vixie, Rodney Joffe, and Frederico Neves. Additionally, Tony Finch, Ted Lemon, John Levine, Jinmei Tatuya, Bob Harold, and Duane Wessels provided valuable feedback and suggestions.