Your company has two domain controllers that are configured as internal DNS servers. All
zones on the DNS servers are Active Directory-integrated zones. The zones allow all
dynamic updates.
You discover that the contoso.com zone has multiple entries for the host names of
computers that do not exist.
You need to configure the contoso.com zone to automatically remove expired records.
What should you do?

A.
Enable only secure updates on the contoso.com zone,

B.
Enable scavenging and configure the refresh interval on the contoso.com zone.

C.
From the Start of Authority tab, decrease the default refresh interval on the contoso.com
zone.

D.
From the Start of Authority tab, increase the default expiration interval on the
contoso.com zone

Explanation:
http://www.it-support.com.au/configure-aging-and-scavenging-of-a-dns-server/2012/12/
Configure aging and scavenging of a DNS Server
Resource records that are either outdated or decayed from DNS zone data are removed
through the use of the Server aging and scavenging feature in Windows Server 2008. Issues
develop if decayed resource records are not dealt with, such as:
Zone transfers take longer as the DNS server disk space contains a large number of stale
records
The accumulation of stale records degrades the DNS server performance and response time
Potential conflicts can occur, if an IP address in a dynamic DNS environment is assigned to
a different host. By default, the aging and scavenging feature is disabled. In order to use this
particular feature, the user is required to enable the operations on the zone and at the DNS
server.
In addition, a user is able to manually enable individual resource records to be aged and
scavenged. This process involves permitting the records to use the current (non-zero)
timestamp value.
The aging and scavenging operation figures out when the records should be cleared by
reviewing their timestamps. The DNS Server uses a simple equation when setting a time
value on a record: current server time + refresh interval.
Procedure:
Navigate to Start – Administrative Tools – DNS Manager. Right click the relevant DNS server
and select Set Aging/Scavenging for All Zones from the drop down list.

The Server Aging/Scavenging Properties dialog box opens. Tick the option Scavenge stale
resource records.
Under the No-refresh interval heading, specify the duration for which the server must not
refresh its records.
Configuring this setting reduces replication traffic as unnecessary updates to existing
records are prevented.
Under the Refresh interval heading, specify the duration for which the server must refresh its
records. The fresh interval is the time required between when a no-refresh interval expires
and when a record is considered stale.
When you have configured these settings, click OK to continue.

A confirmation box appears showing a summary of your settings. Tick the Apply these
settings to the existing Active Directory-integrated zones option and click OK.

The Aging and Scavenging intervals have now been configured for all zones managed by
the DNS server.
http://blogs.technet.com/b/networking/archive/2008/03/19/don-t-be-afraid-of-dns-scavengingjust-bepatient.aspx
Don’t be afraid of DNS Scavenging. Just be patient.
http://social.technet.microsoft.com/Forums/en-US/winserverNIS/thread/bb556cfb-3217-4dcfaf4f-460366faa1b8 Answered Best Practices configuration for DNS server on Windows 2008
R2 Server (aging/scavenging, etc.)