Three kinds of addresses exist in IPv6: unicast, multicast and anycast. Unicast addresses are used for communications between two nodes. A unicast address is a one-to-one address. Multicast addresses are used for communications between one node and many nodes and anycast addresses are used for communications between one node and the nearest node among a group of nodes.
Multicast addresses start with ‘ff’ as the leftmost octet. Any other value of the leftmost octet (‘00’ to ‘fe’) identifies a unicast address. Anycast addresses are formed using the unicast address space, so they cannot be distinguished from unicast addresses.
Global addresses are used for communications between nodes on the Internet. They are the normal addresses that every node uses. These addresses, called global unicast addresses [RFC 3513], are currently assigned as 001 as the 3 leftmost bits in the 128 bit address. This corresponds to addresses from 2000:: to 3fff:ffff:ffff:ffff:ffff:ffff:ffff:ffff, or 2000::/3.
This address space has been defined to use the leftmost 64 bits for the network prefix and the rightmost 64 bits for the host part. So, except in specific cases, all subnets in IPv6 have the same prefix length of 64 bits (/64). The host part, now precisely named as the interface identifier because hosts and interfaces may have multiple addresses, is based on the IEEE EUI-64 standard described in Section 5.2.1.
Important to remember:
All subnets in the global ...