The service can use the two-message exchange method to assign IPv6 addresses and other network configuration parameters to clients only when two-message exchange is enabled on the DHCPv6 clients and server. Otherwise, the server assigns IPv6 addresses and other network configuration parameters to the clients using the four-message exchange method.
To modify the DHCPv6 address autoconfiguration mode, you must disable the original mode. For example, the DHCPv6 client is enabled to use the stateful DHCPv6 address autoconfiguration mode to obtain an IPv6 address and other network configuration parameters including the IPv6 addresses of the DNS and SNTP servers. To enable the DHCPv6 client to use the stateless DHCPv6 address autoconfiguration mode to obtain network configuration parameters (excluding IPv6 addresses), run the undo ipv6 address auto dhcp command to disable stateful DHCPv6 address autoconfiguration and then run the dhcpv6 client information-request command to enable stateless DHCPv6 address autoconfiguration.