Networking / Beginners

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Configuring Dynamic Updates with DHCP

By default, post-Windows 2000 DHCP clients attempt to perform dynamic updates of their host (A) resource records in DNS whenever an address event (such as an address renewal) occurs. However, these same clients do not attempt to perform dynamic updates of their PTR resource records; instead, post-Windows 2000 DHCP clients request that the DHCP server attempt to update their PTR resource records in DNS on behalf of the client.

Default DNS Update Settings for DHCP Servers

By default, a DHCP server registers records on behalf of a DHCP client only according to client request. That is, because the DHCP client by default requests that the server update only the client's PTR resource records, the DHCP server attempts only this type of update. However, a server can also be configured to attempt an update of both A and PTR resource records, regardless of the client request. This behavior is determined by the settings on the DNS tab of the DHCP server properties dialog box.

Note These settings can also be configured in the scope properties dialog box or the reservation properties dialog box.

When the Enable DNS Dynamic Updates According To The Settings Below check box is selected, which is the default, dynamic update is enabled for the DHCP server. When it is enabled, either of two options is specified. If the first option, the default, is selected, the DHCP server attempts to update resource records only according to the client's request. When you select the second option, the DHCP server always attempts to update the client's A and PTR resource records after an address event, regardless of the client request. However, this setting is significant only for DHCP clients capable of requesting dynamic updates, including computers running Windows 2000, Windows XP, or Windows Server 2003.

When you clear the Enable DNS Dynamic Updates According To The Settings Below check box, the DHCP server never attempts dynamic updates on behalf of Windows 2000, Windows XP, or Windows Server 2003 clients.

Another setting you can configure on the DNS tab of the DHCP server properties dialog box is the Discard A And PTR Records When Lease Is Deleted check box. By default, this check box is selected, which means that the DHCP server removes clients' resource records from DNS when their DHCP address leases are deleted. However, by clearing this check box, you can configure the DHCP server to leave client records in DNS even when a client's DHCP address lease is deleted.

The final dynamic update setting you can configure on this tab determines whether the DHCP server should provide dynamic DNS update service on behalf of DHCP clients not capable of performing dynamic updates, such as computers running Microsoft Windows NT 4. By default, Windows Server 2003 DHCP servers do not attempt to per form dynamic updates on behalf of these clients. To modify this default behavior, select the appropriate (lowest) check box on the DNS tab of the server properties dialog box.