The master browser maintains the browse list, the list of all servers in the master browser's domain or workgroup, and the list of all domains on the network. For a domain that spans more than one subnetwork, the master browser maintains the browse list for the portion of the domain on its subnetwork.
Individual servers announce their presence to the master browser by sending a directed datagram called a server announcement to the domain or workgroup's master browser. Computers running Windows NT Server, Windows NT Workstation, Windows for Workgroups, and LAN Manager servers send server announcements. When the master browser receives a server announcement from a computer, it adds that computer to the browse list.
The master browser also returns lists of backup browsers (in the local subnetwork of a TCP/IP-based network, if the domain spans more than one subnetwork) to computers running Windows NT Server, Windows NT Workstation, and Windows for Workgroups. If a TCP/IP subnetwork comprises more than one domain, each domain has its own master browser and backup browsers. On networks using the NetBEUI Frame (NBF) or NWLink IPX/SPX-compatible network protocol, name queries are sent across routers, so there is always only one master browser for each domain.
When a computer starts and the computer's MaintainServerList registry entry is set to Auto, the master browser must tell that computer whether or not to become a backup browser.
When a computer first becomes a master browser, it can force all servers to register with it if its browse list is empty. The master browse computer does this by broadcasting a RequestAnnouncement datagram. All computers that receive a RequestAnnouncement datagram must respond by sending a server announcement at a random time within the next 30 seconds. The randomized delay ensures that the network and the master browser itself are not overwhelmed with responses.
When a master browser receives a server announcement from another computer that claims to be the master browser, the receiving master browser demotes itself and forces an election. This action ensures that there is always only one master browser in each domain or workgroup.
Note The list of servers that the master browser maintains is limited to 64K of data. This limits the number of computers that can be in a browse list in a single workgroup or domain to 2000-3000 computers.