CCENT/CCNA ICND1 100-101 Official Cert Guide

Address Ranges for Global Unicast Addresses

Global unicast addresses make up the majority of the IPv6 address space. However, unlike IPv4, the rules for which IPv6 address fall into which category are purposefully more flexible than they were with IPv4 and the rules for IPv4 Classes A, B, C, D, and E.

Originally, IANA reserved all IPv6 addresses that begin with hex 2 or 3 as global unicast addresses. (This address range can be written succinctly as prefix 2000::/3.)

Later RFCs made the global unicast address range wider, basically to include all IPv6 addresses not otherwise allocated for other purposes. For example, the unique local unicast addresses, discussed later in this chapter, all start with hex FD. So, while global unicast addresses would ...