Find available network resources
When you click the Network Neighborhood icon on your desktop or select it from Windows NT Explorer, you can step down to a list of domains. From this list, you can drill down further to a list of computers in a domain, then a list of shared resources on a particular computer. The browser service generates these lists. You might have noticed that the list of domains is sometimes incomplete first thing in the morning and that the browser service consumes a lot of network bandwidth.
In this article, I explain how the browser service works and why it consumes so much bandwidth. I also suggest ways to reduce the network traffic associated with this service. (For more information about the browser service, see George Spalding, "Too Many Servers Spoil Network Performance," August 1997, and Bob Chronister, Tricks & Traps, September 1996.)
The Browser Service
The browser service has nothing to do with the Internet. This service compiles and distributes lists of available resources on the network. As Screen 1, page 172, shows, when you connect to Network Neighborhood from your computer, the browser service shows you a list of the other computers on your network from which you can drill down to see available resources. The idea behind the browser service is that when a computer needs to see the available resources on the network, it doesn't have to query every other computer on the network. This method would create an overwhelming load on the network and computers. Instead, a few computers known as browsers are responsible for compiling a list of available resources, distributing this list to other browsers, and making the list available to all the other computers on the network. This activity occurs in the background, as a service running under NT. Windows 98, Win95, and Windows for Workgroups (WFW) computers also browse for resources, but not as a service. You can start and stop browsing, like any service, from the Services applet in Control Panel.
Browser Roles
Several types of browsers exist. A computer can participate in the browsing process as a master browser, backup browser, browser candidate, or nonbrowser.
A master browser is the computer that compiles the list of available resources and makes the list available to the backup browsers. Each subnet has a master browser, because browsing is based on broadcasts. Broadcasts don't go through routers, so each subnet requires a master browser. The Primary Domain Controller (PDC) acts as a domain's master browser, coordinating browse lists from the other master browsers.
A backup browser is one of several computers that keep copies of the resource list and supply the list to client computers. You might not need a backup browser in a small network, but most midsized to large networks have one or more backup browsers. The master browser, rather than the administrator, determines the number of backup browsers.
A browser candidate (or potential browser) is a computer that can act as a master or backup browser. By default, NT computers are browser candidates, so they can be backup browsers unless you configure them to not participate. A computer such as a database server isn't suitable to be a backup browser because it can't handle the additional load necessary to support the browsing process. Thus, you'll want to configure it as a nonbrowser.
A nonbrowser isn't part of the browsing process. You must specifically configure a computer to be a nonbrowser.
Browser Election
Most of the time, you have no control over whether a system is the master browser or a backup browser. Browser election determines the master browser, and browser election occurs in the following two situations.
If a client computer can't find a master browser, it calls an election and simultaneously broadcasts its qualifications to be a master browser. Other computers on the network see this election packet and compare it with their qualifications. The process then proceeds much like a poker game: If a machine has higher qualifications, it sends out an election packet. Finally, the machine with the highest qualifications wins. In this context, highest qualifications means that NT beats Win98, NT 4.0 beats NT 3.51, server beats workstation, and so on. Thus, the master browser is typically an NT 4.0 server. Just as in a real election or a real poker game, other factors can influence the outcome. NT has favorites: A domain controller typically wins any election in which it participates, and the PDC always wins in a network with subnets because only a PDC can be a domain master browser.
A browser election also occurs when a domain controller comes online. If you look at the NT System event log on the domain controller, you'll see that a forced browser election occurred when this computer started. Screen 2 shows the event log entry. If you have more than one protocol running, you'll see more than one entry.