Configuring scavenging in Windows Server 2008



A notebook user’s computer, for example, may update its host record in its zone, but then the user disconnects from the network without shutting down. The computer remains off the network for an extended period, but the computer’s host record still remains in the zone. As a result, the record becomes stale and potentially points to the wrong IP address (or the user may change computer’s host name). You can configure Windows Server 2008 DNS to scavenge records, removing those that are stale.

Windows Server 2008 uses a timestamp to determine whether a record is stale. The server scans the data at an administrator-defined interval, checking the resource records’ timestamps to determine whether they have exceeded the refresh interval. If so, the server scavenges the record (removes it from the zone). Scavenging, by default, applies only to dynamically created records and has no effect on records that you create manually. The DNS server, however, applies a timestamp to resource records that you create manually, setting the timestamp to zero to indicate that the record is not subject to scavenging. You can alter the value to allow the DNS service to scavenge these records as well.

You can configure scavenging in two places: at the server level and at the zone level. At the server level, you can allow scavenging globally for the server and set the scavenging frequency, how often the server performs scavenging. The default value is seven days, and the minimum is one hour. To configure scavenging at the server level, open the DNS console, right-click the server, and choose Properties. Click the Advanced tab to display the Advanced property page.

Select the Enable Automatic Scavenging of Stale Records option and then use the Scavenging Period control to specify how often the server should perform a scavenging operation. The more dynamic the network, the more frequently you should have the server perform scavenging. Choose a value that fits your network requirements.

Also you need to configure scavenging on a zone-by-zone basis. Scavenging can be applied only to primary zones. Open the DNS console, right-click the zone for which you want to configure scavenging, and choose Properties. On the zone’s General property page, click Aging to open the Zone Aging/Scavenging Properties dialog box.

The dialog box includes the following two controls:

1) No-Refresh Interval: This property essentially specifies the timestamp’s time-to-live. Until this period expires, the record’s timestamp can’t be refreshed.

2) Refresh Interval: This property defines the period of time that the timestamp can remain un-refreshed before the server scavenges the record.

Scavenging occurs automatically at the interval defined in the server’s general scavenging properties. You can also manually initiate a scavenge. Open the DNS console, right-click the server, and choose Scavenge Stale Resource Records.