170DHCPv6 overviewDHCPv6 provides a framework to assign IPv6 prefixes, IPv6 addresses, and other configurationparameters to hosts.DHCPv6 address/prefix assignmentAn address/prefix assignment process involves two or four messages.Rapid assignment involving two messagesAs shown in Figure 49, rapid assignment operates in the following steps:1. The DHCPv6 client sends to the DHCPv6 server a Solicit message that contains a RapidCommit option to prefer rapid assignment.2. If the DHCPv6 server supports rapid assignment, it responds with a Reply message containingthe assigned IPv6 address/prefix and other configuration parameters. If the DHCPv6 serverdoes not support rapid assignment, Assignment involving four messages is performed.Figure 49 Rapid assignment involving two messagesAssignment involving four messagesAs shown in Figure 50, four-message assignment operates using the following steps:1. The DHCPv6 client sends a Solicit message to request an IPv6 address/prefix and otherconfiguration parameters.2. The DHCPv6 server responds with an Advertise message that contains the assignableaddress/prefix and other configuration parameters if either of the following conditions exists:{ The Solicit message does not contain a Rapid Commit option.{ The DHCPv6 server does not support rapid assignment even though the Solicit messagecontains a Rapid Commit option.3. The DHCPv6 client might receive multiple Advertise messages offered by different DHCPv6servers. It selects an offer according to the receiving sequence and server priority, and sends aRequest message to the selected server for confirmation.4. The DHCPv6 server sends a Reply message to the client, confirming that the address/prefixand other configuration parameters are assigned to the client.
