Active Directory 2008: Aging and Scavenging Facts…

Aging and Scavenging Facts

Dynamic updating can cause your zones to become overloaded with unnecessary resource records. If a computer disconnects improperly from the network (as is often the case when you allow mobile users and computers on your network), the host (A) resource record it registered may not be removed. It is for reasons such as this that DNS records have a Time to Live (TTL) value. When a record exceeds its TTL, it becomes stale. Large numbers of stale records can cause long zone transfers and name resolution problems. Stale records can also degrade DNS server performance. A stale record may also prevent a computer from using a DNS domain name.

Scavenging is controlled through a combination of DNS server and zone properties.

Setting Description
Zone properties On the zone, enable scavenging and   configure the following settings:

  • The no-refresh interval        is the time between the record’s last refresh and when it can next be        refreshed. By default, this setting is 7 days. This means that for seven        days, DNS ignores a record’s attempt to re-register itself, keeping        replication to a minimum. During this period of time, a record is        considered valid and cannot be refreshed.
  • The refresh interval        identifies a period of time when a record can be refreshed. The refresh        interval begins when the no-refresh interval ends. During the refresh        interval, a record can be refreshed and is not considered stale until        this interval of time expires. A resource record is not scavenged until        the refresh interval expires. The default refresh interval is 7 days.

You can configure zone scavenging   settings for all zones by right-clicking the server and selecting Set   Aging/Scavenging for all zones.

DNS server properties Scavenging must be initiated to   actually remove any records that have not been refreshed since the refresh   interval has expired. To initiate scavenging:

  • Manually initiate it by        right-clicking the server and selecting Scavenge Stale Resource        Records.
  • Enable automatic scavenging        by editing the server properties. On the Advanced tab, select Enable        automatic scavenging of stale records. The default is for scavenging        to run once a day.

Note: Scavenging is only configured on primary zones. After you enable scavenging on a zone, the zone file cannot be used on another DNS server.

Be aware of the following when configuring scavenging:

  • Each      DNS record has a default refresh setting. The record will attempt to      refresh itself based on this interval. The default for an A record is 7      days.
  • The      no-refresh interval for the zone should be set with a value that is equal      to (or less than) the longest record refresh interval.
  • The      refresh interval for the zone should be set to a value that is longer than      the longest record refresh interval. If not, some records might be deleted      before the record attempts to refresh itself.
  • The      difference between zone scavenging and server scavenging is that zone      scavenging is applied to a single zone where server scavenging is applied      to an entire server.

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