To understand the process of aging and scavenging at the server, consider the life span and successive stages of a single resource record, as it is added to a server and zone where this process is in effect and then aged and removed from the database.
A sample DNS host, "hosta.example.microsoft.com", registers its host (A) resource record at the DNS server for a zone where aging/scavenging is enabled for use.
When registering the record, the DNS server places a time stamp on this record, based on current server time.
After the record time stamp is written, the DNS server does not accept refreshes for this record for the duration of the zone no-refresh interval. It can, however, accept updates prior to that time. For example, if the IP address for "host-a.example.microsoft.com" changes, the DNS server can accept the update. In this case, the server also updates (resets) the record time stamp.
Upon expiration of the no-refresh period, the server begins to accept attempts to refresh this record.
Once the initial no-refresh period ends, the refresh period immediately begins for the record. During this time, the server does not suppress attempts to refresh the record for its remaining life span.
During and after the refresh period, if the server receives a refresh for the record, it processes it.
This resets the time stamp for the record based on the method described in step 2.
When subsequent scavenging is performed by the server for the "example.microsoft.com" zone, the record (and all other zone records) are examined by the server.
Each record is compared to current server time on the basis of the following sum to determine whether the record should be removed:
Record time stamp + No-refresh interval for zone + Refresh interval for zone
If the value of this sum is greater than current server time, no action is taken, and the record continues to age in the zone.
If value of this sum is less than current server time, the record is deleted both from any zone data currently loaded in server memory and also from the applicable DnsZone object store in Active Directory for the directory-integrated "example.microsoft.com." zone.