Windows 2000 Professional on Microsoft Networks
After users log on to the network, they need to locate shared resources. Windows 2000 provides shared resources by publishing objects in domains and by using the browse function in server message block (SMB)–based networks, such as Windows NT.
Publishing Objects in Active Directory
Publishing is the act of creating Active Directory objects that directly contain the information you want to make available or that provide a reference to it. For example, a user object contains useful information about users, such as their telephone numbers and e-mail addresses, and a volume object contains a reference to a shared file system volume. Published objects are available to Windows 2000–based, Windows 95–based, and Windows 98–based clients that have Active Directory client software installed. Publishing can only be implemented in an Active Directory domain where TCP/IP is the transport protocol.
The following provides two examples of publishing file and print objects in Active Directory:
Share publishing. Network administrators and authenticated users can publish a shared folder as a volume object (also called a shared folder object) in Active Directory by using the Active Directory Users and Groups snap-in. This means that users can now easily and quickly query Active Directory for a shared folder.
Printer publishing. In a Windows 2000 domain, the easiest way to manage, locate, and connect to printers is through Active Directory. When you add a printer by using the Add Printer wizard and you elect to share the printer, Windows 2000 Server publishes it in the domain as an object in Active Directory. Publishing (listing) printers in Active Directory lets users locate the most convenient printer. Users can now easily query Active Directory for any of these printers, searching by printer attributes, such as type (PostScript, color, legal-sized paper, and so on) and location. When you remove a printer from the server, it is unpublished by the server.
The Windows 2000 operating system introduces the global catalog , a database that resides on one or more domain controllers. The global catalog plays major roles in logging on users and querying.
In an enterprise that contains many domains, the global catalog allows clients to quickly and easily perform searches across all domains without having to search each domain individually. The global catalog makes directory structures within an enterprise transparent to end users seeking information.
Computer Browser and Browsing Roles
The Computer Browser service provides a method of locating shared resources within a domain or workgroup environment. Computers running the Server service (which includes both workstations and servers) announce their availability by means of broadcast messages, which are captured by computers designated as browsers . The function of the browser is to create, maintain, and distribute a browse list , which is a directory of all shared resources used on the network.
Browsing is required by network applications that use SMB block messaging in Windows 2000 and previous versions of Windows, such as My Network Places, the net view command, and Windows NT Explorer.
Domains that allow browsing are likely to be controlled by computers running earlier versions of Windows operating systems, such as Windows 98 or Windows NT. For purposes of compatibility, Windows 2000 domains support browsing with clients that use these operating systems; however, you can enhance the functionality of browsing by publishing shared resources in Active Directory and in global catalogs.
In an environment that supports browsing, computers can perform the following roles:
Domain master browser
Master browser
Backup browser
Potential browser
Nonbrowser
Table 23.3 describes the browser roles and functions that computers operating this service can perform.
Table 23.3 Browser Roles and Functions
Browser Role |
Function |
|---|---|
Domain master browser |
Used only in domain environments. By default, the primary domain controller (PDC) for a domain operates in this role. Collects and maintains the master browse list of available servers for its domain, as well as any names for other domains and workgroups used in the network. Distributes and synchronizes the master browse list for master browsers on other subnets that have computers belonging to the same domain. A Windows 2000 Professional–based computer cannot become a domain master browser. |
Master browser |
Collects and maintains the list of available network servers in its subnet. Fully replicates its listed information with the domain master browser to obtain a complete browse list for the network. 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 upon request. |
Potential browser |
Under normal conditions, operates similarly to a nonbrowser. Capable of becoming a backup browser if instructed to by the master browser for the subnet. This is the default configuration for a Windows 2000 Professional–based computer. |
Nonbrowser |
Does not maintain a browse list. Can operate as a browse client, requesting browse lists from other computers operating as browsers on the same subnet. Configured so it cannot become a browser. |
Under some 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 of operation. This is typically performed through a process known as browser election .
When a Windows 2000 Professional–based computer starts up, it first checks the registry entry MaintainServerList to determine whether a computer can become a browser. This entry is found in:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Browser\Parameters
Table 23.4 describes the values that you can assign to the MaintainServerList entry to specify how a computer participates in browser services.
Table 23.4 Allowable Values for the MaintainServerList Registry Entry
Value |
Description |
|---|---|
No |
Prevents the computer from participating as a browser. |
Yes |
Makes the computer a browser. Upon 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. The master browser notifies the computer whether it is to become a backup browser. |
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Tip
It is a good idea to set the MaintainServerList entry to No on computers that are frequently powered off or removed from the network, such as portable computers. This ensures that a browse server is always available and helps to reduce browser elections. 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 2000 Professional 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 2000 Professional–based computer is False .
Browser Elections
After the browsing role for a Windows 2000 Professional–based computer is determined, the computer checks to see if a master browser is already 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. Browser elections occur under the following circumstances:
When a computer cannot locate a master browser.
When a preferred master browser comes online.
When a Windows NT domain controller starts.
If a master browse server already exists, Windows 2000 checks the number of computers in the workgroup and the number of browse servers present. If the number of computers in the workgroup exceeds the defined ratio of browse servers to computers (usually one browse server for every 32 computers) and the MaintainServerList registry entry is set to Auto , the master browser can select a Windows 2000 Professional–based computer to act as a backup browser.
For more information about the selection criteria used in browser elections, see Browser Service in the Microsoft Windows 2000 Server Resource Kit TCP/IP Core Networking Guide.
Building the Browse List for Microsoft Networks
In Windows 2000 Professional, the browse service maintains an up-to-date list of domains, workgroups, and computers and provides this list to applications when requested. The user sees the list in the following circumstances:
If a user requests a list of computers in a workgroup, the browse service on the local computer randomly chooses a browse server and sends the request.
If a user selects a workgroup in which the users computer does not belong:
Windows 2000 Professional requests a list of the computers that belong in the selected workgroup, obtaining the list from a browse server in the selected workgroup.
The selected browse server also sends a list of the workgroups that are on the network and a list of computers in the users workgroup.
The browse list is displayed anywhere that Windows 2000 Professional presents lists of browsable resources. The browse list can also be displayed by using the net view command. 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, 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 MS-DOS peer servers.
LAN Manager 2. x domains and servers.
Adding New Computers to the Browse List
When a computer running Windows 2000 Professional is started on the network, it announces itself to the master browse server for its workgroup, and the master browse server adds that computer to the list of available computers in the workgroup. The master browse server then notifies backup browse servers that a change to the browse list is available. The backup browse servers then request the new information to update their local browse lists. It might take as long as 15 minutes before a backup browse server receives an updated browse list, and new computers on the network do not show up in a users request for a browse list until after this time period.
Removing Computers from the Browse List
When a user shuts down a computer properly, the operating system informs the master browse server that it is shutting down. The master browse server then notifies backup browse servers that a change to the browse list is available. The backup browse servers then request the changes to the browse list.
If a user turns off the computer without shutting down, the computer does not get a chance to send the message to the master browse server. In such cases, the computer name continues to appear in the browse list until the name entry times out, which can take up to an hour.