[BCP109]   Best Current Practice 109,
              <https://www.rfc-editor.org/info/bcp109>.
              At the time of writing, this BCP comprises the following:

              Huston, G., "Deprecation of "ip6.int"", BCP 109, RFC 4159,
              DOI 10.17487/RFC4159, August 2005,
              <https://www.rfc-editor.org/info/rfc4159>.