Managing the aging and scavenging of server data

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Managing the aging and scavenging of server data

Aging and scavenging of stale resource records are features of DNS available when deploying your server with primary zones.

Where aging and scavenging are available for use, you can use the DNS console to perform the following related tasks for your DNS servers and any directory-integrated zones that they load:

  1. Enable or disable the use of scavenging at a DNS server.

  2. Enable or disable the use of scavenging for selected zones at the DNS server.

  3. Modify the no-refresh interval, either as a server default or by specifying an overriding value at selected zones.

  4. Modify the refresh interval, either as a server default or by specifying an overriding value at selected zones.

  5. Specify whether periodic scavenging occurs automatically at the DNS server for any of its eligible zones, and how often these operations are repeated.

  6. Manually initiate a single scavenging operation for all eligible zones at the DNS server.

  7. View other related properties, such as the time stamp for individual resource records or the start scavenging time for a specified zone.

Enabling scavenging of stale resource records

By default, aging and scavenging features are disabled on all DNS servers and any of their zones. Before using these features, you should configure these settings for the applicable server and its directory-integrated zones:

  • Server aging/scavenging properties  for determining the use of these features on a server-wide basis.

    First, you need to enable aging and scavenging of stale resource records for use at the server. These settings are used to determine the affect of zone-level properties for any directory-integrated zones loaded at the server.

    For more information, see Set aging/scavenging properties for the DNS server.

  • Zone aging/scavenging properties  for determining the use of these features on a per-zone basis.

    When zone-specific properties are set for a selected zone, these settings apply only to the applicable zone and its resource records. Unless these zone-level properties are otherwise configured, they inherit their defaults from comparable settings maintained in server aging/scavenging properties.

    For more information, see Set aging/scavenging properties for a zone.

Modifying no-refresh intervals

When the no-refresh interval is in effect for a specific resource record, attempts to dynamically refresh its time stamp are suppressed by the DNS server. This aspect of the aging/scavenging mechanism prevents unnecessary refreshes from being processed by the server for aged resource records. These early refresh attempts, if not handled in this way, might otherwise increase Active Directory replication traffic related to processing DNS zone changes.

To ensure that records do not refresh prematurely, keep the No-refresh interval comparable in length to the current refresh interval for each resource record. For example, if you increase the Refresh interval to a higher value you can similarly increase the no-refresh interval.

In most instances, the default interval of 7 days is sufficient and does not need to be changed.

Modifying refresh intervals

When the refresh interval is in effect for a resource record, attempts to dynamically refresh its time stamp are accepted and processed by the DNS server. When setting this interval, it is important that the length of time used be greater than the maximum possible refresh period for any resource records contained within the zone. This period is equal to the maximum amount of time that it might take the record to be refreshed under normal network conditions, based on the specific source generating the record refresh.

For example, the following table shows default refresh periods for various services known to dynamically register and refresh records in DNS:

Service Default refresh period

Net logon

24 hours

Clustering

24 hours

DHCP client

24 hours

Note

  • The DHCP Client service sends dynamic updates for the DNS records. This includes both computers that obtain a leased IP address using DHCP and those that are configured statically for TCP/IP.

DHCP server

4 days (half of the lease interval, which is 8 days by default)

Note

  • Refresh attempts are only made by the DHCP servers configured to perform DNS dynamic updates on behalf of their clients (for example Windows 2000 Server DHCP server and Windows Server 2003 DHCP server). The period is based on the frequency in which DHCP clients renew their IP address leases with the server. Typically, this occurs when 50% of the scope lease time has elapsed. If the DNS default scope lease duration of 8 days is used, then the maximum refresh period for records updated by DHCP servers on behalf of clients is 4 days.

By default, the refresh interval is 7 days. In most instances, this value is sufficient and does not need to be changed, unless any resource records in the zone are refreshed less often than every 7 days.

Automated and manually-initiated scavenging

Although scavenging start time and other factors determine when zones and records are actually eligible for scavenging, you have the option to perform scavenging using either of two methods to initiate it:

  • Automatic scavenging  specifies that aging and scavenging of stale records is to be performed automatically by the server for any eligible zones at a recurring interval specified as the scavenging period. When using automatic scavenging, the default scavenging period is 1 day and the minimum allowed value you can use is 1 hour.

    For more information, see Enable automatic scavenging of stale resource records.

  • Manual scavenging  specifies that aging and scavenging of stale records is to be performed as a non-recurring operation for any eligible zones at the server.

    For more information, see Start immediate scavenging of stale resource records.

Modifying time stamp values

For resource records that are not dynamically added to DNS zone data, a record time stamp value of zero is applied, preventing these records from aging or removal during scavenging.

You can, however, manually reset record properties to enable any statically entered records to qualify for the aging/scavenging process. If you do this, the record will be deleted based upon the modified time stamp value, at which point, you might need to recreate a record if it is still needed.

For more information, see Reset scavenging and aging properties for a specified resource record.

Caution

  • Enabling aging and scavenging for use with standard primary zones modifies the format of zone files. This change does not affect zone replication to secondary servers, but the modified file cannot be loaded by other versions of DNS servers.

  • Before using information in this topic, be sure that you have reviewed the aging/scavenging process and use of its configurable properties and features. For more information, see Understanding aging and scavenging.

Note