IPv6 Address Autoconfiguration

A major feature of IPv6 is a host's ability to autoconfigure an interface. Through Neighbor Discovery, the host locates an IPv6 router on the local link and requests a site prefix. The host does the following, as part of the autoconfiguration process:

• Creates a link-local address for each interface, which does not require a router on the link.

• Verifies the address's uniqueness on a link, which does not require a router on the link.

• Determines if the global addresses should be obtained through the stateless mechanism, the stateful mechanism, or both mechanisms. (Requires a router on the link.)

Stateless Autoconfiguration Overview

Stateless autoconfiguration requires no manual configuration of hosts, minimal (if any) configuration of routers, and no additional servers. The stateless mechanism enables a host to generate its own addresses. The stateless mechanism uses local information as well as nonlocal information that is advertised by routers to generate the addresses.

You can implement temporary addresses for an interface, which are also autoconfigured. You enable a temporary address token for one or more interfaces on a host. However, unlike standard, autoconfigured IPv6 addresses, a temporary address consists of the site prefix and a randomly generated 64 bit number. This random number becomes the interface ID portion of the IPv6 address. A link-local address is not generated with the temporary address as the interface ID.

Routers advertise all prefixes that have been assigned on the link. IPv6 hosts use Neighbor Discovery to obtain a subnet prefix from a local router. Hosts automatically create IPv6 addresses by combining the subnet prefix with an interface ID that is generated from an interface's MAC address. In the absence of routers, a host can generate only link-local addresses. Link-local addresses can only be used for communication with nodes on the same link.

Do not use stateless autoconfiguration to create the IPv6 addresses of servers. Hosts automatically generate interface IDs that are based on hardware-specific information during autoconfiguration. The current interface ID could become invalid if the existing interface is swapped for a new interface.