The primary domain controller (PDC) of a domain is given a bias in browser elections to ensure that it becomes the master browser. The browser service running on a domain's primary domain controller has the special additional role of being the domain master browser.
For a domain that uses TCP/IP and spans more than one subnetwork, each subnetwork functions as an independent browsing entity, with its own master browser and backup browsers. To browse across the WAN to other subnetworks, at least one browser running Windows NT Server is required on the domain for each subnetwork. On the subnetwork with the PDC, this Windows NT Server computer is typically the PDC, which functions as the domain master browser.
When a domain spans multiple subnetworks, the master browsers for each subnetwork announces itself as the master browsers to the domain master browser using a directed MasterBrowserAnnouncement datagram. The domain master browser then sends a remote NetServerEnum API call to each master browser to collect each subnetwork's list of servers. The domain master browser merges the server list from each subnetwork master browser with its own server list to form the browse list for the domain. This process is repeated every 15 minutes to ensure that the domain master browser has a complete browse list of all the servers in the domain.
The master browser on each subnetwork also sends a remote NetServerEnum API call to the domain master browser to obtain the complete browse list for the domain. This browse list is thus available to browser clients on the subnetwork.
Note Windows NT workgroups cannot span multiple subnetworks. Any Windows NT workgroup that spans subnetworks actually functions as two separate workgroups, with identical names.