H3C Technologies H3C S12500 Series Switches - Manual (Page 180)

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Assignment involving four messages
Figure 67 shows the process of IPv6 address/prefix assignment involving four messages.
Figure 67 Assignment involving four messages
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 the DHCPv6 server does not
support rapid assignment though a Rapid Commit option is contained, 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 might 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 use the IPv6 address/prefix longer, the DHCPv6 client has to renew
the lease time.
Figure 68 Using the Renew message for address/prefix lease renewal
As shown in Figure 68 , at T1, the DHCPv6 client sends a Renew message to the DHCPv6 server to renew
its address and prefix lease. The recommended value of T1 is half the preferred lifetime. Then the
DHCPv6 server responds with a Reply message, informing that the lease is renewed or not.