[STD57]    Internet Standard 57,
              <https://www.rfc-editor.org/info/std57>.
              At the time of writing, this STD comprises the following:

              Malkin, G., "RIP Version 2 Protocol Applicability
              Statement", STD 57, RFC 1722, DOI 10.17487/RFC1722,
              November 1994, <https://www.rfc-editor.org/info/rfc1722>.