When using domains that are split across routers, each TCP/IP network segment functions as an independent browsing entity with its own master browser and backup browsers. Therefore, browser elections occur within each network segment.
Domain master browsers are responsible for spanning the network segments to collect computer-name information, in order to maintain a domain-wide browse list of available resources. The domain master browser and cooperating master browsers on each WAN segment provide browsing of domains that exist across multiple TCP/IP network segments. The domain master browser is the PDC of a domain. The master-browser computers on the subnets can be running Windows NT Server, Windows NT Workstation, Windows for Workgroups version 3.11b, or Windows 95.
Figure 3.8 Browser service across a WAN
When a domain spans multiple network segments, the master browsers for each network segment use a directed datagram called a MasterBrowserAnnouncement datagram to announce themselves to the domain master browser. The MasterBrowserAnnouncement datagram notifies the domain master browser that the sending computer is a master browser in the same domain and that the domain master browser needs to obtain a copy of the master browser's browse list. When the domain master browser receives a MasterBrowserAnnouncement datagram, it sends a request to the network segment's master browser, which announced itself in order to collect a list of the network segment's servers.
The domain master browser then merges its own server list with the server list from the master browser that issued the announcement. This process is done every 15 minutes and guarantees that the domain master browser has a complete browse list of all the servers in the domain. When a client issues a browse request to a backup browser, the backup browser returns a list of all the servers in the domain, regardless of the network segment on which they are located.
Workgroup using Windows NT or Windows for Workgroups cannot span multiple network segments. Any workgroup of either kind that does span network segments will function as two separate workgroups with the same name.