[BCP168]   Best Current Practice 168,
              <https://www.rfc-editor.org/info/bcp168>.
              At the time of writing, this BCP comprises the following:

              Le Faucheur, F., Ed., "IP Router Alert Considerations and
              Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October
              2011, <https://www.rfc-editor.org/info/rfc6398>.