Scavenge Properties for DNS

The DNS server performs queries and then stores the results of those queries as part of the zone database files. Over time the size of a DNS database can really grow. Because of the nature of host name records, they will change over time. IP addresses are changed, names are changed, or both. It doesn't make sense to simply keep resolved queries in the zone database file indefinitely. Instead, it is desirable that you age records in the database and then scavenge them out of the database when they are no longer valid. This is where things get a little tricky. How long should a record stay in DNS? How old is too old? What is the usable life of a cached DNS record? Windows Server 2008 R2 uses two values associated with aging and scavenging called the refresh interval and the no-refresh interval.

• The refresh interval is the time between the NN earliest moment when a record timestamp can be refreshed and the earliest moment when the record can be scavenged. By default this value is set to seven days. The question is, "Is seven days the right value?" The answer is, "Probably!" We know that is not really an answer, but in most cases seven days will work just fine. If you have a reason to change the value, you are more than welcome to do so. Please do not feel like you have to keep the default value if something else will work better for your network.
• The no-refresh interval is the time between the most recent refresh of a record timestamp and the moment when the record can be refreshed again. This value is also set by default to seven days. Like the refresh interval, the no-refresh interval can be changed to suit the needs of your organization. In layman's terms, the no-refresh interval is really just a definition of how long DNS should wait until it refreshes a record. You want to make sure that your DNS server is not constantly refreshing records. Once a record is refreshed, the norefresh interval defines how long to wait until the record is refreshed.

You can change both of these values using DNS Manager:

1. Open DNS Manager.
2. Right-click the DNS Server, and choose Set Aging/Scavenging for all zones.
3. Select Scavenge Stale Resource Records. (This is not enabled by default.)
4. Change the no-refresh interval to your desired value.
5. Change the refresh interval to your desired value.