When When an IPv4 DHCP client sends DHCP DISCOVER and DHCP REQUEST messages, it can include option 81, the Client FQDN option. An IPv6 DHCP client can include option 39, the Client FQDN option, when it sends Solicit and Request messages.
The Client FQDN option contains the FQDN (fully qualified domain name) of the client and instructions on whether the client or the server performs DDNS updates. You can configure the appliance to replace the FQDN in the option by defining a hostname rewrite policy. For information about adding and enabling a hostname rewrite policy, see Replacing Host Names for DDNS Updates.
The DHCP server can support option 81 for IPv4 and IPv6 clients, and use the host name or FQDN that the client provides for the update. It can also allow or deny the client's request to update DNS, according to the administrative policies of your organization. The DHCP server indicates its response in the DHCP OFFER message it sends back to an IPv4 client, and in the Reply message it sends back to an IPv6 client.
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- When an IPv4 or IPv6 DHCP client sends a DHCP request with the FQDN option, it can include either its FQDN or only its host name.
- If the request includes the FQDN, the DHCP server uses this FQDN to update DNS. You can specify a list of forward-mapping zones to be updated for IPv4 and IPv6 clients using the FQDN option. For information, see Sending Updates for DHCP Clients Using the FQDN Option.
- If the request includes the host name, the DHCP server provides the domain name. It combines the host name of the client and the domain name to create an FQDN for the client. It then updates DNS with the FQDN it created. (You can enter the domain name in the General page of the DHCP Properties window. For information, see Enabling DDNS for IPv4 and IPv6 DHCP Clients5.)
- When a DHCP client sends a DHCP request with its hostname, the DHCP server adds the domain name you specified to create an FQDN for the client. It then updates DNS with the FQDN it created. For information about entering the domain name, see Enabling DDNS for IPv4 and IPv6 DHCP Clients5.
- When a DHCP client does not send a host name, the DHCP server provides a lease but does not update DNS. You can configure the DHCP server to generate a host name and update DNS as described in Generating Host Names for DDNS Updates9.
- If multiple DHCP clients specify the same FQDN or host name, the DHCP server allocates leases to the clients, but updates DNS only for the client that first sent the request. When it tries to update DNS for the succeeding clients, the update fails.
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Sending Updates from DHCP Clients or a DHCP Server
When you enable the DHCP server to support the FQDN option, you must decide if you want the DHCP server to allow clients to update DNS. If you allow the client to update DNS, then the client updates its A or AAAA record only. The DHCP server always updates the PTR records. You can configure the DHCP server as follows:
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- Enable support for the option and specify who performs the DDNS update. For more information, see Enabling FQDN Option Support.
- Specify the DNS zones and DNS view for the updates. For more information, see Sending Updates for DHCP Clients Using the FQDN Option.
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You can configure support for the FQDN option for IPv4 and IPv6 clients at the Grid, member, network and shared network levels.
To configure support for the FQDN Option (option 81) for IPv4 and (Option 39) for IPv6:
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