DHCP Interoperability with DNS

Updated: November 10, 2008

Applies To: Windows Server 2008

A DHCP server running Windows Server 2008 can perform dynamic updates in the DNS namespace for any of its clients that support these updates. Scope clients can then use the DNS dynamic update protocol to update their host name-to-address mapping information, which is stored in zones on the DNS server, whenever changes occur to their DHCP-assigned addresses.

The DHCP server can be used to register and update the pointer (PTR) and host (A) resource records on behalf of its DHCP-enabled clients. This process requires the use of an additional DHCP option, the Client FQDN option (option 81), which permits the client to provide its fully qualified domain name (FQDN) as well as instructions to the DHCP server on how the server should process DNS dynamic updates, if any, on its behalf.

When this option is issued by a qualified DHCP client, such as a DHCP-enabled computer running Windows Vista, option 81 is processed and interpreted by the DHCP server to determine how the server initiates updates on behalf of the client. If the server is configured to perform DNS dynamic updates, it takes one of the following actions:

  • The DHCP server updates both DNS A and PTR records if requested by clients using option 81.

  • DHCP server updates DNS A and PTR records regardless of whether the client requests this action.

In addition, the DHCP server can dynamically update DNS A and PTR records on behalf of legacy clients that are not capable of sending option 81 to the server. You can also configure the DHCP server to discard client A and PTR records when the client lease is deleted.

You can configure the DHCP server in one of the following ways:

  • Update at client request: The DHCP server registers and updates client information with the authoritative DNS server of the zone in which the DHCP server is located only if the DHCP client requests it. This is the default configuration for DHCP servers running Windows Server 2008 and DHCP clients running Windows 2000, Windows XP, or Windows Vista. In this mode, the DHCP client can request the way in which the DHCP server performs updates of its host (A) and pointer (PTR) resource records. If possible, the DHCP server accommodates the client request for handling updates of its name and IP address information in DNS.

  • Always update: The DHCP server always registers and updates client information in DNS. This is a modified configuration supported for DHCP servers running Windows Server 2008 and DHCP clients running Windows 2000, Windows XP, or Windows Vista. In this mode, the DHCP server always performs updates of the client's FQDN, leased IP address information, and both its host (A) and pointer (PTR) resource records, regardless of whether the client has requested to perform its own updates.

  • Never update: The DHCP server never registers and updates client information in DNS. To set this behavior, the DHCP server must be configured to disable performance of DHCP/DNS proxied updates. By disabling this feature, no client host (A) or pointer (PTR) resource records are updated in DNS for DHCP clients.

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