[BCP157]   Best Current Practice 157,
              <https://www.rfc-editor.org/info/bcp157>.
              At the time of writing, this BCP comprises the following:

              Narten, T., Huston, G., and L. Roberts, "IPv6 Address
              Assignment to End Sites", BCP 157, RFC 6177,
              DOI 10.17487/RFC6177, March 2011,
              <https://www.rfc-editor.org/info/rfc6177>.