Valid

Time

Preferred Lifetime

Valid Lifetime

Figure 8-1 The states of an autoconfigured address

Note With the exception of autoconfiguration for link-local addresses, address autoconfiguration is specified only for hosts. Routers must obtain address and configuration parameters through another means, such as manual configuration.

Autoconfiguration Process

The address autoconfiguration process defined in RFC 4862 for the physical interface of an IPv6 node is the following:

1.A tentative link-local address is derived based on the link-local prefix of FE80::/64 and a EUI-64–derived interface identifier.

2.Using duplicate address detection to verify the uniqueness of the tentative link-local address, a Neighbor Solicitation message is sent with the Target Address field that is set to the tentative link-local address.

3.If a Neighbor Advertisement message (sent in response to the Neighbor Solicitation message) is received, this indicates that another node on the local link is using the tentative link-local address and address autoconfiguration stops. At this point, manual configuration must be performed on the node.

4.If no Neighbor Advertisement message (sent in response to the Neighbor Solicitation message) is received, the tentative link-local address is assumed to be unique and valid. The link-local address is initialized for the interface. The link-layer multicast address of the solicited-node address corresponding to the link-local address is registered with the network adapter.

For an IPv6 host, the address autoconfiguration continues as follows:

1.The host sends a Router Solicitation message. While routers periodically send router advertisements, the host sends a Router Solicitation message to request an immediate router advertisement, rather than waiting until the next router advertisement. By default, up to three Router Solicitation messages are sent.

194Understanding IPv6, Second Edition

2.If no Router Advertisement messages are received, the host uses an address configuration protocol to obtain addresses and other configuration parameters.

3.If a Router Advertisement message is received, the hop limit, reachable time, retransmission timer, and maximum transmission unit (if that option is present) are set.

4.For each Prefix Information option present, the following actions occur:

If the On-Link flag is set to 1, the prefix is added to the prefix list.

If the Autonomous flag is set to 1, the prefix and an appropriate interface identifier are used to derive a tentative address.

Duplicate address detection is used to verify the uniqueness of the tentative address.

If the tentative address is in use, the use of the address is not initialized for the interface.

If the tentative address is not in use, the address is initialized. This includes setting the valid and preferred lifetimes based on the Valid Lifetime and Preferred Lifetime fields in the Prefix Information option. If needed, it also includes registering the link-layer multicast address of the solicited-node address corresponding to the new address with the network adapter.

5.If the Managed Address Configuration flag in the Router Advertisement message is set to 1, an address configuration protocol is used to obtain additional addresses.

6.If the Other Stateful Configuration flag in the Router Advertisement message is set to 1, an address configuration protocol is used to obtain additional configuration parameters.

Figures 8-2 and 8-3 show the address autoconfiguration process for a host.

In RFC 4862, the address configuration protocol for stateful autoconfiguration is DHCPv6.

For an example of IPv6 stateless address autoconfiguration based on an exchange of Router Solicitation and Router Advertisement messages, see Network Monitor capture 08_01 in the \NetworkMonitorCaptures folder on the companion CD-ROM.

Figure 8-2 The address autoconfiguration process for a host (Part 1)