Just wanted to add a note on the above.
While the Aging intervals can be reduced in the GUI to a few short hours, you should never set the Refresh Interval lower than 24 hours. Systems with static IP addresses, including your Domain Controllers and any other servers, will be dynamically registering records and performing a Refresh once every 24 hours.
Therefore, setting a Refresh Interval lower than 24 hours will result in the removal of valid records for your servers, and a lot of hassle for you.
I agree with PaciB's conclusion, increasing the DHCP lease would be preferable if you can. If you'd like an example, my settings are these:
DHCP Lease: 16 days
No-Refresh: 4 days
Refresh: 4 days
Automatic Scavenging: Once every day
The total aging time matches up to the DHCP Renewal interval (50% of lease, 8 days).
Chris
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by: PaciBPosted on 2009-10-30 at 02:00:47ID: 25701106
Hi,
DNS Scavenging can permit you to keep a "clean" DNS zone by deleting old records. "Old records" means DNS records that are obsolete for many days or week, not for hours...
Scanvenging is not really dynamic and won't delete a record as soon as it is unused... It will takes days before the record to be deleted.
Scavenging setting need at least two parameters (I'm not sure of english translation of these settings cause I'm using french version of Windows) :
- The "refresh prohibit" period (7 days by default) : When a DNS record is created or refreshed, then it cannot be refreshed again (meaning the timestamp can nont be updated) for 7 days.
- The "grace period before delete" (7 days by default) : If a DNS records is not refreshed for 7 days (meaning the timestamp is 7 days old) then it is deleted.
The first period ("refresh prohibit") is made to limit the numbre of AD object replication because with AD integrated DNS zones, DNS records are AD objects and then each timestamp refresh is an AD object modification. Dynamic DNS registration may then provocate too much object modification in AD. To avoid that, by default, a DNS record refuse new timestamp refresh for 7 days since the last refresh.
So, in fact, an unused DNS record will be deleted 14 days after it's last refresh if you configure scavenging with default settings (7 days + 7 days).
You can reduce these periods but don't expect for a really fast cleaning of the DNS zone. You can probably reduce periods to 3 days + 3 days. That will avoid DNS records to be deleted after the week-end.
In fact, may be you DHCP lease time is too short... 12 hours is very short. But it can be justified if you have a lot of external laptops that occasionally connect on your network. If not, you can probably increase the DHCP lease to some days... 4 days is a usually a good value.
Have a good day.