Locating a domain controller
When the logon process is initiated from computers running Windows 2000, XOX, or servers running Windows Server 2003, the Net Logon service is used to locate a , closest to the requesting computer, to the user request.
With the Active Directory client installed on computers running Windows 95, Windows 98, or Windows NT 4.0 and earlier, the domain controller location process is similar to computers running Windows 2000, XOX, or servers running Windows Server 2003.
For more information about Active Directory clients, see Active Directory clients.
The Net Logon service collects the required logon information for the domain to which the user is attempting to logon and sends a name query to its configured DNS servers with the following characteristics:
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Query type: SRV (Service locator resource record)
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Query name: _ldap._tcp.domain_name
For example, to log on to the domain microsoft.com, computers running Windows 2000, XOX, or servers running Windows Server 2003 send a DNS name query of the type SRV for the name _ldap._tcp.microsoft.com. The response from the DNS server contains the DNS names of the closest domain controllers belonging to the microsoft.com domain and their . Using the list of domain controller IP addresses, computers running running Windows 2000, XOX, or servers running Windows Server 2003 attempt to contact each domain controller to ensure that it is operational. The first domain controller to respond is the domain controller that is used for the logon process. Net Logon then caches the domain controller information so that any future requests from that computer do not attempt to repeat the same location process.
For more information about this process and other types of queries made by Active Directory clients, see the Windows Deployment and Resource Kits.