Locating Resources by Publishing Objects

Typically, users want to locate shared resources when they log on to the network. Windows XP Professional provides shared resources by publishing objects in domains and by using the browse function in SMB-based networks, such as Windows NT.

Publishing

Publishing is the act of creating objects in Active Directory that either contain the information you want to make available or that provide a reference to that information. For example, a user object contains useful information about the user, such as a telephone number and an e-mail address. Similarly, a volume object might contain a reference to a shared file system volume. Published objects are available to Windows XP Professional based and Windows 2000 based clients, and to Windows NT 4.0 based, Windows 95 based, and Windows 98 based clients that have Active Directory client software installed. Publishing can be implemented only in an Active Directory domain where TCP/IP is the transport protocol.

Share publishing and printer publishing are two examples of file and print objects published in Active Directory.

Share publishing

Network administrators and authorized users can publish a shared folder as a shared folder object in Active Directory by using the Active Directory Users and Computers snap-in of the Microsoft Management Console (MMC). Users can then query Active Directory for a shared folder.

Printer publishing

In a Windows 2000 or Windows Server 2003 domain, Active Directory simplifies managing, locating, and connecting to printers. When you add a printer by using the Add Printer wizard, and then share the printer, Windows 2000 Server publishes it in the domain as an object in Active Directory. Publishing printers in Active Directory lets users locate the most convenient printer. Users can now query Active Directory for any of these printers by specifying printer attributes such as type (PostScript or legal-sized paper, for example) and location. When you remove a printer from the server, it is unpublished by the server.

Computer Browser and Browsing Roles

The Computer Browser service provides a method of locating shared resources within a domain or workgroup environment. The service transparently designates certain workstations or servers as browse servers, which maintain master browse lists, or directories of all shared resources on the network. The Computer Browser service designates other workstations and servers as browsers, which contact the nearest browse server to obtain the master browse list.

Browsing is required by network applications that use SMB, such as My Network Places, the net view command, and Windows Explorer.

Typically, domains that allow browsing are controlled by computers that run earlier versions of Windows operating systems, such as Windows 98 or Windows NT. For compatibility, Windows 2000 and Windows Server 2003 domains support browsing for clients that use these operating systems. However, you can enhance the functionality of browsing by publishing shared resources to Active Directory and to global catalogs.

Table 20-1 describes the browser roles and functions that computers using this service can perform.

Table 20-1: Browser Roles and Functions

Browser Role	Function
Domain master browser	A browse server that collects and maintains the master browse list of available network servers for its domain, as well as any names for other domains and workgroups used in the network. The domain master browser distributes and synchronizes the master browse list for master browsers on other subnets that have computers belonging to the same domain. It is used only in domain environments. By default, the primary domain controller for a domain has this role. A Windows XP Professional based computer cannot become a domain master browser but it can function as a browse server.
Master browser	A browse server that collects and maintains the list of available network servers in its subnet. The master browser replicates its listed information by relying on the domain master browser to obtain a complete browse list for the network. This browser then distributes its completed list to backup browsers located on the same subnet.
Backup browser	Receives a copy of the browse list from the master browser for its subnet. Distributes the browse list to other computers on request.
Potential browser	Under normal conditions, operates similarly to a nonbrowser. It is capable of becoming a backup browser if instructed to by the master browser for the subnet. This is the default configuration for a Windows XP Professional based computer.
Nonbrowser	Can operate as a browse client, requesting browse lists from other computers that have browser roles on the same subnet. However, it does not maintain a browse list. It is configured so it cannot become a browser.

Under certain conditions, such as failure or shutdown of a computer that is designated for a specified browser role, browsers or potential browsers might change to a different role by using a process known as browser election.

When a Windows XP Professional based computer starts, it checks the registry entry MaintainServerList to determine if it can become a browser. This entry is found in:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Browser\ Parameters

Table 20-2 describes the values that you can assign to the MaintainServerList entry to specify how a computer participates in browser services.

Table 20-2: Allowable Values for the MaintainServerList Registry Entry

Value	Description
No	Prevents the computer from participating as a browser.
Yes	Makes the computer a browser. At startup, the computer attempts to contact the master browser to get a current browse list. If the master browser cannot be found, the computer forces a browser election. The computer becomes either an elected master browser or a backup browser.
Auto	Makes the computer a potential browser. It might become a browser, depending on the number of currently active browsers. If necessary, the master browser instructs the computer if it must become a backup browser. The Auto value is the default for computers running Windows XP Professional, Windows 2000 Professional, and Windows NT Workstation 4.0.

Tip 

Set the MaintainServerList entry to No on computers that are frequently turned off or removed from the network, such as portable computers. This ensures that a browse server remains available, helps to reduce browser elections, and reduces network overhead caused by a browser. Disabling browsing on client computers also reduces the network overhead that results from browser announcements.

Another entry in this registry location, IsDomainMaster, determines if a Windows XP Professional based computer can become a preferred master browser. A preferred master browser has priority over other computers in master browser elections. Whenever a preferred master browser starts, it forces an election. The default setting for a Windows XP Professional based computer is False.

Caution 

Do not edit the registry unless you have no alternative. The registry editor bypasses standard safeguards, allowing settings that can damage your system, or even require you to reinstall Windows. If you must edit the registry, back it up first and see the Registry Reference in the Microsoft Windows 2000 Server Resource Kit at http://www.microsoft.com/reskit

Browser Elections

After the browsing role for a Windows XP Professional based computer is determined, the computer checks to see if a master browser is present on the domain. If a master browse server does not exist, a browser election determines which computer becomes a master browse server for the workgroup. A browser election occurs when the following circumstances exist:

• A computer cannot locate a master browser.

• A preferred master browser comes online.

• A Windows NT based domain controller starts.

  Note 

  In a Computer Browser service context, a server is any computer that can provide resources to the rest of the network. For example, a computer that can share files or print resources with other computers on the network is considered a server in the context of the browser system even if the computer is not actively sharing resources.

If a master browse server already exists, Windows XP Professional checks the number of computers in the workgroup and the available browse servers. If the number of computers in the workgroup exceeds the defined ratio of browse servers to computers (typically one browse server for every 32 computers), and the MaintainServerList registry entry is set to Auto, the master browser can select a Windows XP Professional based computer to act as a backup browser.

Building the Browse List for Microsoft Networks

In Windows XP Professional, the Computer Browser service maintains an up-to-date list of domains, workgroups, and computers and provides this list to applications at the user s request. The user sees the list in the following circumstances:

• If a user requests a list of computers in a workgroup, the Computer Browser service on the local computer randomly chooses a browse server and sends the request.

• If a user selects a workgroup to which the user s computer does not belong:

  • Windows XP Professional requests a list of the computers that belong to the selected workgroup. A browse server in the selected workgroup provides the list.

  • The selected browse server sends a list of the workgroups that are on the network and a list of computers in the user s workgroup.

The browse list is displayed anywhere that Windows XP Professional presents lists of browsable resources. You can also use the net view command to view the browse list. The list can contain the names of domains, workgroups, and computers that run the file and printer sharing service, including the following:

• Computers running Windows 98, Windows 95, Microsoft Windows for Workgroups, and Windows NT Workstation.

• Windows NT domains and servers.

• Workgroups defined in Windows 98, Windows 95, Windows for Workgroups, Windows NT Server, and Windows NT Workstation.

• Workgroup Add-on for Microsoft MS DOS peer servers.

• LAN Manager 2.x domains and servers.