[STD33]    Internet Standard 33,
              <https://www.rfc-editor.org/info/std33>.
              At the time of writing, this STD comprises the following:

              Sollins, K., "The TFTP Protocol (Revision 2)", STD 33,
              RFC 1350, DOI 10.17487/RFC1350, July 1992,
              <https://www.rfc-editor.org/info/rfc1350>.