[BCP128]   Best Current Practice 128,
              <https://www.rfc-editor.org/info/bcp128>.
              At the time of writing, this BCP comprises the following:

              Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
              Cost Multipath Treatment in MPLS Networks", BCP 128,
              RFC 4928, DOI 10.17487/RFC4928, June 2007,
              <https://www.rfc-editor.org/info/rfc4928>.