H3C Technologies H3C S10500 Series Switches - Manual (Page 140)

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Assignment involving four messages
Figure 51 shows the process of IPv6 address/prefix assignment involving four messages.
Figure 51 Assignment involving four messages
The assignment involving four messages operates in the following steps.
1. The DHCPv6 client sends out a Solicit message, requesting an IPv6 address/prefix and other
configuration parameters.
2. If the Solicit message does not contain a Rapid Commit option, or if the DHCPv6 server does not
support rapid assignment even though the Solicit message contains a Rapid Commit option, the
DHCPv6 server responds with an Advertise message, informing the DHCPv6 client of the
assignable address/prefix and other configuration parameters.
3. The DHCPv6 client may receive multiple Advertise messages offered by different DHCPv6 servers.
It then selects an offer according to the receiving sequence and server priority, and sends a
Request message to the selected server for the confirmation of assignment.
4. The DHCPv6 server sends a Reply message to the client, confirming that the address/prefix and
other configuration parameters are assigned to the client.
Address/prefix lease renewal
The IPv6 address/prefix assigned by the DHCPv6 server has a lease time, which depends on the valid
lifetime. When the valid lifetime of the IPv6 address/prefix expires, the DHCPv6 client cannot use the
IPv6 address/prefix any longer. To continue using the IPv6 address/prefix, the DHCPv6 client has to
renew the lease time.
Figure 52 Using the Renew message for address/prefix lease renewal
As shown in Figure 52 , at T1, the DHCPv6 client unicasts a Renew message to the DHCPv6 server that
assigned the IPv6 address/prefix to the DHCPv6 client. The recommended value of T1 is half the
preferred lifetime. Then the DHCPv6 server responds with a Reply message, informing the client about
whether or not the lease is renewed.