IPv6 Global Address Structure

IPv6 global addresses are equivalent to Public IP addresses in IPv4 and are globally reachable on the IPv6 portion of the Internet. The global IPv6 address structure is divided into three parts, the Public and Private routing part, and the host identification within a LAN. These parts add up to 128 bits which are structured as follows:

The first 48 bits of the address are the global routing prefix specifying the organization’s network with the first 3 bits of this prefix must be 001 in binary notation. These 48 bits represent the public topology portion of the address which represents the collection of large and small ISPs on the IPv6 Internet and which is controlled by these ISPs through assignment by the IANA (Internet Assigned Numbers Authority).

The next 16 bits are the subnet ID. The organization can use this portion to specify up to 65,536 unique subnets for routing purposes inside the internal network. These 16 bits represent the internal network portion of the address which the organization has control over.

The final 64 bits are the interface ID and specify a unique interface within each subnet. This interface ID is equivalent to a host IP in IPv4.

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