DNS > Automatically Removing Out Dated Resource Records

While the ability of DHCP to register A and PTR resource records automatically whenever a new device is added to the network makes life easier for the network administrator, it does have one drawback: Unless action is taken to remove them, those resource records will remain in the DNS zone database indefinitely.

While this is not a problem with relatively static networks, it negatively affects networks that change frequently (with the addition and removal of portable computers, for example). This accumulation of records can result in poor performance of both the DNS server and DHCP services as both have to work around these stale (obsolete) host/address mappings.

Eventually, the zone could even run out of addresses for computers that are subsequently added to the network.
Fortunately, Windows DHCP services and the Windows Server 2003 DNS server are designed to cooperate to help prevent this from happening. You can configure the DNS server to track the age of each dynamically assigned record and to periodically remove records older than a specified number of days, a process known as scavenging.

The age of a record is based on when it was created or last updated. By default, computers running Windows 2000, Windows XP, and Windows Server 2003 send a request to the DNS server to update their records every 24 hours. (To prevent unnecessary replication, the Windows Server 2003 DNS server can be configured to ignore these requests for a period of time.) The DNS server is thereby notified that the computers in question are still on the network and their records are not subject to scavenging.

Because scavenging can cause problems on a network when it is misconfigured, it is disabled by default in Windows Server 2003. Enabling scavenging with default settings is quite safe and is recommended if computers are frequently added to and removed from your network.

To enable scavenging on a DNS server :

1. At the DNS server you want to enable scavenging on, click Start, point to Administrative Tools, and then click DNS.
2. In the console tree, click the applicable DNS server.
3. On the Action menu, click Properties.
4. Click the Advanced tab, select Enable automatic scavenging of stale records, and then click OK.
5. On the Action menu, click Set Aging/Scavenging for All Zones, click Scavenge stale resource records, and then click OK.
6. In the Server Scavenging/Aging Confirmation dialog box, select Apply these settings to the existing Active Directory-enabled zones, and then click OK.