[BCP207]   Best Current Practice 207,
              <https://www.rfc-editor.org/info/bcp207>.
              At the time of writing, this BCP comprises the following:

              Hardaker, W., Gudmundsson, O., and S. Krishnaswamy,
              "DNSSEC Roadblock Avoidance", BCP 207, RFC 8027,
              DOI 10.17487/RFC8027, November 2016,
              <https://www.rfc-editor.org/info/rfc8027>.