Login and Domain Database Replication

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Login and Domain Database Replication

Windows NT network services also performs other tasks that initiate broadcasts to all computers in the domain (see Figure 10.13). Two of these tasks are described as follows:

Logging on to a domain and password changes. A broadcast message is sent out from the client computer to find a domain controller that can provide authentication of the login or find the primary domain controller to allow changing of the user’s password.
Domain controllers replicating the domain user account database. The primary domain controller sends a broadcast to the backup domain controllers, telling them it has changes to the account database they need to update to themselves.

The preceding items are important to understand because they are broadcasts and therefore do not cross IP routers on their own. You have to utilize directed traffic instead. A broadcast initiated to perform these jobs is also given to the remote domain controllers. The list of remote domain controllers is decided by what is listed in either the LMHOSTS file or the WINS database.

When the client needs to access a domain controller, it broadcasts the message directly to the domain and looks for any #DOM: entries in its LMHOSTS file that matches the domain name. If it finds an identical entry it sends the message specifically to that computer.

It is probably a good idea to add remote domain controller #DOM: entries into the LMHOSTS file with an identical domain name to each client. If the domain controller ever goes down, the users are still able to access remote domains and log on. This is also useful if there are no local domain controllers to enable users to log in to a domain controller on a remote subnet.

LMHOSTS files are generally for non-WINS clients. You can still reference these non-WINS clients by using a WINS proxy agent, enabling a WINS server to add a non-WINS client to its database through the use of an additional machine that updates the WINS server in place of the non-WINS client. Proxy servers are covered lightly in the following section but are not mentioned anymore as they are a topic all their own and not tested in this exam.

All the backup domain controllers should have #DOM: entries for the primary domain controller, as well as all other backup domain controllers. This way, if one gets promoted to the primary domain controller the backup domain controllers still have mappings to the new primary domain controller.

Overall, WINS provides the better solution for accessing multiple domains and workgroups over different subnets, provided, of course, that all systems are WINS-compliant: Windows 95, Windows NT, Windows for Workgroups with TCP/IP 32 add on.

Further Information

WINS Proxy Agent

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