IPv6 Unicast Addressing

The IPv6 global aggregatable unicast address, also known as the IPv6 global unicast address, is the equivalent of the IPv4 global unicast address. A global unicast address is an IPv6 address from the global unicast prefix. These global unicast addresses are designed in a way so that their prefixes can be reduced making for more efficient routing due to a decreased routing table size. Global unicast addresses used on links are aggregated upward through organizations and eventually to the ISP's. This also allows for more efficient and scalable routing within the Internet, an improved bandwidth and functionality for user traffic.

A global unicast address typically consists of a 48-bit global routing prefix, a 16-bit subnet ID, and a 64-bit interface ID that's usually in the EUI-64 bit format.The subnet field is similar to the IPv4 subnets, organizations can use the subnet ID to create their own local addressing hierarchy. This field allows an organization to use up to 65,536 individual subnets!

The current global unicast address assignment by the Internet Assigned Numbers Authority (IANA) uses the range of address that start with the binary value 001 (2000::/3). This is one-eighth of the total IPv6 address space and is the largest block of assigned addresses. The IANA then allocates the 2001::/16 prefixes to the registries.

IPv6 Link-Local addressing have a scope limited to the local link and are dynamically created on all IPv6 interfaces by using the specific link-local prefix FE80::/10 and a 64-bit interface identifier. Link-local addresses are used for automatic address configuration, neighbor discovery, router discovery, and by different routing protocols.