Aging and Scavenging of Stale Records

With dynamic update, records are automatically added to the zone when computers and domain controllers are added. However, in some cases, they are not automatically deleted. For example, if a computer registers its own A resource record and is improperly disconnected from the network, the A resource record might not be deleted. If your network has many mobile users, this can happen frequently.

Having many stale resource records presents a few different problems. Stale resource records take up space on the server, and a server might use a stale resource record to answer a query. As a result, DNS server performance suffers.

To solve these problems, the Windows 2000 DNS server can "scavenge" stale records; that is, it can search the database for records that have aged and delete them. Administrators can control aging and scavenging by specifying the following:

• Which servers can scavenge zones

• Which zones can be scavenged

• Which records must be scavenged if they become stale

The DNS server uses an algorithm that ensures that it does not accidentally scavenge a record that must remain, provided that you configure all the parameters correctly. By default, the scavenging feature is off.

Caution

By default, the scavenging mechanism is disabled. Do not enable it unless you are absolutely certain that you understand all the parameters. Otherwise, you might accidentally configure the server to delete records that it should retain. If a name is accidentally deleted, not only do users fail to resolve queries for that name, but also, any user can create that name and then take ownership of it, even on zones configured for secure dynamic update.

You can manually enable or disable aging and scavenging on a per-server, per-zone, or per-record basis. You can also enable aging for sets of records by using the command line tool Dnscmd.exe. (For information about Dnscmd.exe, see Windows 2000 Support Tools Help. For information about installing and using the Windows 2000 Support Tools and Support Tools Help, see the file Sreadme.doc in the directory \Support\Tools on the Windows 2000 operating system CD.) Keep in mind that if you enable scavenging on a record that is not a dynamic update record, the record will be deleted if it is not periodically refreshed, and you must recreate the record if it is still needed.

If scavenging is disabled on a standard zone and you enable scavenging, the server does not scavenge records that existed before you enabled scavenging. The server does not scavenge those records even if you convert the zone to an Active Directory–integrated zone first. To enable scavenging of such records, use the AgeAllRecords in Dnscmd.exe.