About Configuration Manager Discovery
Within Microsoft System Center Configuration Manager 2007, once you've installed your central Configuration Manager site, you'll want to begin adding clients and resources to the site. These are added using one of the available Configuration Manager discovery methods, which search your network to find resources that you can use with Configuration Manager 2007. You must use at least one discovery method before you can use most Configuration Manager functionality. In short, it's necessary to "discover" computers on your network before you can install the Configuration Manager 2007 client software that allows you to deliver packages, updates, and so forth to those clients.
Resources
Although many of these discovered resources are computers on which you can install the client software, other resources can also be discovered and added to the Configuration Manager database. These other resources include Active Directory objects (such users, groups, and computers), as well as other site systems, routers, hubs, printers, and other IP-addressable devices on your network.
For a more in-depth discussion of resources within Configuration Manager 2007, see About Resources.
Discovery Methods
Six methods of discovery are available in Configuration Manager 2007:
Network Discovery
Heartbeat Discovery
Active Directory System Group Discovery
Active Directory Security Group Discovery
Active Directory System Discovery
Active Directory User Discovery
The most commonly used, however, will probably be Network Discovery, as it's the most generalized form of discovery. It allows Configuration Manager 2007 to perform a broad search of your network by checking the DHCP leases, looking at routers' Address Resolution Protocol (ARP) caches, or looking for SNMP)-enabled devices in a community. Because of the broad spectrum of resources connected to your network, network discovery is also likely to find resources such as printers that are not capable of becoming Configuration Manager 2007 clients.
Configuration Manager 2007 can also communicate with Active Directory to locate resources such as computer accounts, user accounts, system groups, and security groups already existing in your accounts database.
Configuration Manager 2007 also uses Heartbeat Discovery, but instead of it being used to create new database records, it is used to keep existing records up to date. Heartbeat Discovery is the only configurable discovery method that is automatically enabled when Configuration Manager 2007 is installed.
Configuration Manager 2007 also creates database records for site server and site system computers when you assign a site system role to that computer, as well as when inventory is collected from a Configuration Manager client. This method of discovery is automatic and not configurable.
Database Records
As Configuration Manager 2007 discovers resources, it creates records in the Configuration Manager database. This record is called a data discovery record (DDR) and the file generated has a .DDR extension. The specific information contained in each record varies depending on the resource "discovered," but it can include data such as the NetBIOS name of a computer, IP address and IP subnet of a computer or device, operating system, MAC address, and so on.
Depending on the discovery method used, resource DDRs are periodically regenerated to keep the discovery data up to date in the database and to verify that the resource is still a valid resource within the Configuration Manager 2007 site.