DNS Aging and Scavenging
NoRefresh + Refresh + Scavenge period => Refresh and No-refresh intervals. Both of these must elapse before a record can be deleted.
The No-refresh interval is a period of time during which a resource record cannot be refreshed.
Recall from earlier that a refresh is a dynamic update where we are not changing the host/IP of a resource record, just touching the timestamp.
If a client changes the IP of a host record this is considered an “update” and is exempt from the No-refresh interval.
The purpose of a No-refresh interval is simply to reduce replication traffic. A change to a record means a change that must be replicated.
If you right-click on your server you will see the option to “Set Aging/Scavenging for All Zones…”. Selecting this will take you to a screen similar to the one above. What does this do? This sets the default settings that will be used if a new zone is created by this server. Unless you check the subsequent box “Apply these settings to the existing Active Directory-integrated zones” it will not touch existing zones.
The Scavenging Period is how often this particular server will attempt to scavenge. When a server scavenges it will log a DNS event 2501 to indicate how many records were scavenged. An event 2502 will be logged if no records were scavenged. Only one server is required to scavenge since the zone data is replicated to all servers hosting the zone.
Example:
- The zone is set to a 3-day Refresh and a 3-day No-Refresh interval
- The server Scavenging period is set to 3 days
- The last DNS Event id 2501 or 2502 occurred at 6 am on 12-Nov-20230
- We have a record with a timestamp of 12-Nov-2023 at 12:00 noon
We can predict that the record will be deleted at approximately 6 am on 22-Nov-2023.
https://web.archive.org/web/20160428150734/https://blogs.technet.microsoft.com/networking/2008/03/19/dont-be-afraid-of-dns-scavenging-just-be-patient/#