[BCP5]     Best Current Practice 5,
              <https://www.rfc-editor.org/info/bcp5>.
              At the time of writing, this BCP comprises the following:

              Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
              J., and E. Lear, "Address Allocation for Private
              Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
              February 1996, <https://www.rfc-editor.org/info/rfc1918>.