[BCP196]   Best Current Practice 196,
              <https://www.rfc-editor.org/info/bcp196>.
              At the time of writing, this BCP comprises the following:

              Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast
              Prefix for 6to4 Relay Routers", BCP 196, RFC 7526,
              DOI 10.17487/RFC7526, May 2015,
              <https://www.rfc-editor.org/info/rfc7526>.