RFC 1884: “IP Variation six Addressing Architecture” uses that phrase for many bits at the end of an IPv6 address. (The number of bits appeared to vary in some diverse illustrations, but this identifier was commonly determined by the MAC-48 handle of a community card.) If you use this Firefox https://whatsmyipv431974.wikifrontier.com/7293813/not_known_details_about_whatsmyipv4