[BCP146]   Best Current Practice 146,
              <https://www.rfc-editor.org/info/bcp146>.
              At the time of writing, this BCP comprises the following:

              Bellovin, S., "Guidelines for Specifying the Use of IPsec
              Version 2", BCP 146, RFC 5406, DOI 10.17487/RFC5406,
              February 2009, <https://www.rfc-editor.org/info/rfc5406>.