Managing the DHCP Database

Applies To: Windows Server 2008

The DHCP database in Windows Server 2008 uses the Exchange Server Jet storage engine. The DHCP server database is a dynamic database that is updated as DHCP clients are assigned or as they release their TCP/IP configuration parameters. Because it is not a distributed database like the WINS server database, maintaining the DHCP server database is less complex.

There is no set limit to the number of records that a DHCP server can store; the size of the database depends on the number of DHCP clients on the network. The DHCP database grows over time as a result of clients starting and stopping on the network; size of the database is not directly proportional to the number of active client lease entries. Over time, as some DHCP client entries become obsolete and are deleted, some space remains unused.

To recover the unused space, the DHCP database can be compacted. Dynamic database compaction occurs on DHCP servers as an automatic background process during idle time or after a database update.

Maintaining a backup of the DHCP database protects you from data loss if the database is lost due to failure of a hardware component or if it becomes corrupted. The three backup methods supported by the DHCP service are:

  • Synchronous backup: Occurs automatically; the default backup interval is 60 minutes.

  • Asynchronous (manual) backups: Performed using the backup command in the DHCP console.

  • Windows Backup (ntbackup.exe) or other (non-Microsoft) backup software.

When a synchronous or asynchronous backup occurs, the entire DHCP database is backed up, including the following:

  • All scopes, including superscopes and multicast scopes

  • Reservations

  • Leases

  • All options, including server options, scope options, reservation options, and class options

Other configuration settings in the DHCP server properties (such as audit log settings and folder location settings) are stored in the registry and must be backed up using the Registry Editor.

The DNS dynamic update credentials that the DHCP server uses when registering DHCP client computers in DNS cannot be backed up using any backup method.

Synchronous and asynchronous backups are performed while the DHCP service is running. You do not need to stop the DHCP service unless you are moving your database to a new server.

Restoring server data

You can use the Restore method to copy a database to another server. Only DHCP databases from the same language version can be restored. For example, a DHCP database from a server running an English language version of the operating system cannot be restored to a DHCP server running a Japanese language version of the operating system.

To restore the DHCP database, the service must be stopped temporarily. When that happens, DHCP clients will be unable to contact the server and obtain IP addresses until it is restarted.