What Is Computer Browser Service?
Updated: March 28, 2003
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
What Is Computer Browser Service?
Computer Browser service is the mechanism that collects and distributes the list of workgroups and domains and the servers within them. The list displays in the Microsoft Windows Network window and related windows in My Network Places.
Microsoft Active Directory services in Windows Server 2003 and Windows XP create a searchable list of computers and resources that is separate from the list of domains, workgroups, and servers in My Network Places. Computer Browser service provides backward compatibility with computers running earlier versions of Windows that must use Network Basic Input/Output System (NetBIOS) over TCP/IP (NetBT) and are not Active Directory–capable.
In this section
In Windows Server 2003, Computer Browser service is included with Windows Server 2003, Standard Edition; Windows Server 2003, Enterprise Edition; Windows Server 2003, Datacenter Edition; and the 64-bit editions of the Windows Server 2003 family. It is also included in other Windows operating systems as follows:
Microsoft Windows XP
Microsoft Windows 2000
Microsoft Windows Millennium Edition
Microsoft Windows 98
Computer Browser service (and NetBT, which it uses), is enabled by default when any of the above operating systems are installed.
Users often need to know which resources are accessible from their local computers. Computer Browser service enables users to easily browse for available domains, workgroups, servers, and resources in My Network Places. Computer Browser service also provides interoperability with domains and computers that do not use the Active Directory directory service.
In pure Windows Server 2003, Windows XP, and Windows 2000 environments that are configured to use Active Directory, Active Directory itself can display information about available network resources. In Windows 98 and Windows Millennium Edition, however, Computer Browser service must be used for this purpose. Computer Browser service is also still required in Windows Server 2003, Windows XP, and Windows 2000 for using applications such as My Network Places and Windows Explorer, or the net view command.
Computer Browser Service Concepts
Networked computers can play a variety of roles as different types of browse servers. The different types of browse servers and browse clients together are called the browser system.
In versions of Windows that support Computer Browser service, the operating system assigns tasks to specific computers on the network to provide browse services. Any networked computer that can collect, maintain, and distribute a browse list can be a browse server. Computers that are designated as browse servers work together to provide a centralized browse list, which contains a list of all known domains, workgroups, and the set of file servers in the domain to which the computer belongs.
Browse clients on the network access the browse list when users want to view the list of workgroups and domains or the list of servers in a workgroup or domain. For example, when a user at a computer running Windows 98 opens My Network Places, Computer Browser service computer obtains a copy of the browse list from a browse server on the same subnet in order to display the requested list of domains, workgroups, and computers. By working together, browse servers reduce the CPU cycles and network traffic needed to build and maintain the browse list.
When an individual server starts, it announces its presence by sending a broadcast datagram called a host announcement on the subnet. The announcement is received by a master browse server for the workgroup or domain. When the master browse server receives a host announcement from a computer, it adds that computer to the browse list.
When a domain spans more than one subnet, the master browse server:
Maintains the browse list for the portion of the domain on its subnet.
Provides lists of backup browse servers on local subnets of a TCP/IP-based network.
If a TCP/IP-based subnet encompasses more than one domain, each domain has its own master browse server and backup browse servers. On networks using the NWLink IPX/SPX–Compatible protocol, routers forward the NetBIOS over IPX broadcast host announcement packets, a mechanism which allows the network to use only one master browse server.
Whenever a computer starts, if the value of the MaintainServerList entry in its registry is set to Auto, the master browse server must instruct the newly started computer whether to become a backup browse server.
As the master browse server for the network, a computer running Windows Server 2003 contacts the primary domain controller (PDC) every 12 minutes to provide it with the local network’s browse list and to obtain the domain-wide browse list.
For a computer running Windows 98 to be a master browse server, the computer and the PDC for the domain must both be WINS clients. A Windows 98 master browse servermust also:
Use WINS for name resolution.
Be in a workgroup that has the same name as the domain.
Domain Master Browse Server
The domain master browse server:
Collects announcements for the entire domain.
Collects browse lists from master browse servers on other subnets.
Provides a browse list to other master browse servers.
A PDC typically functions as the domain master browse server on its subnet. When Computer Browser service runs on a PDC, the PDC is always the domain master browse server. To ensure that the PDC becomes the domain master browse server, you must give the PDC priority in browse server elections. For information about browse server elections, see “Browser Elections” in How Computer Browser Service Works.
In a domain that uses TCP/IP and that spans more than one subnet, each subnet functions as an independent browsing entity, with each subnet having its own master browse server and backup browse servers. On the other hand, NWLink and NetBEUI Frame (NBF) transports do not use the domain master browse server role; these transports have only a single master browse server for the entire network. When a domain spans multiple subnets, the master browse server of each subnet announces itself as the master browse server to the domain master browse server, using a directed datagram called a MasterBrowserAnnouncement. The domain master browse server then sends a remote NetServerEnum API call to each master browse server, to collect the list of servers from each subnet. The domain master browse server merges the server list from each subnet master browse server with its own server list, forming the server-list portion of the browse list for the domain. This process is repeated every 12 minutes to ensure that the domain master browse server has an updated and complete browse list of all the servers in the domain.
The domain master browse server must be able to resolve the server name of each master browse server on a TCP/IP network (using WINS, for example). Each master browse server must be able to resolve the name of the domain, as well as the computer name of the primary domain controller.
For additional information about Computer Browser service, see Help and Support Center in Windows Server 2003.