So how do browser elections work, what causes them to happen, and how do you keep the number of elections down? In this first installment of my two-part series on browser elections, I offer some answers to these questions.
As I explain in previous articles , Microsoft's Browser Service lets the long-term clients that are still using NetBIOS over TCP/IP (NBT) services on your Windows 2000 network find servers and shared printers. A server in this case is defined as any system running the Server Service, whether or not the system is actually sharing anything. This usually includes just about everyone running any Windows operating system that's NT 4.0 or above. Windows 9x clients turn on the Server Service by asking to share files or printers.
Not all clients on a Windows 2000 network are going to just use DNS. However, in a pure Windows 2000 environment you usually don't need NBT services. Notice the word "usually," because you'll probably be the lucky administrator who has one application or user that needs NBT.
In fact, you're going to be very lucky, if you're in a larger network, to see a pure Windows 2000 environment. Many administrators are not going to get rid of their end users' Windows 95 or 98 systems if those clients have lower system needs. They'll keep older operating systems for budget reasons, if nothing else. They are going to be willing to swap some functionality for financial savings in a time of tightening IT budgets. Usually, this decision is made during the process of designing the Active Directory environment for your network.
So, you've decided that you need NetBIOS over TCP/IP for some of our older clients, and that they will be using the Browser Service. Now, you have to determine how systems get elected to the various roles used in the Browser Service. Let's start with the domain master browser.
About the domain master browser
In an NT 4.0 environment, the PDC registers its domain name with WINS with a <1bh> in the 16th character. This identifies it as the domain master browser.
In a mixed Windows 2000 environment, the PDC emulator registers with WINS as the domain master browser. You can view this by typing nbtstat –n at a command prompt.
If the PDC goes down and causes a domain master browser failure, the administrator is going to have to promote a BDC to PDC. At this point, the new PDC registers as the domain master browser with WINS. The promotion to PDC is not automatic, and must be done by the administrator, but the registration as the new domain master browser is automatic. Since there is a 12-minute interval between registrations with master browsers, it can take a while for the domain master browser to bring its browse list back up to date.
About the master browser
Finally, we get to the meat of browser elections. The master browser is where most election problems take place. (Windows 95 and Windows for Workgroup clients are well-known for constantly thinking they should be master browsers and forcing elections.)
Remember, a master browser is responsible for gathering a list of all systems running the Server Service on their subnet, exchanging this data with the domain master browser, and updating its local browse list with information obtained from the domain master browser pertaining to other subnets and domains. This lets any client see all servers across your enterprise network.
Master browser elections take place under one of three conditions, including when:
- A master browser cannot be located by a computer.
- A computer that has been designated as a preferred master browser comes online.
- A domain controller is brought online.
Then in part two, we'll take an in-depth look at the process of initiating a master browser election and designating one server as a master browser.
About the author: Douglas Paddock, MCSE, MCT, MCSA, is a CIW Security Analyst who is also A+ and N+ certified. He teaches at Louisville Technical Institute in Louisville, Ky.