[BCP164]   Best Current Practice 164,
              <https://www.rfc-editor.org/info/bcp164>.
              At the time of writing, this BCP comprises the following:

              Eastlake 3rd, D., "IANA Considerations for Network Layer
              Protocol Identifiers", BCP 164, RFC 6328,
              DOI 10.17487/RFC6328, July 2011,
              <https://www.rfc-editor.org/info/rfc6328>.