Making sense of browser elections, part two

Why do unwanted browser elections keep popping up on Windows administrator's Event Viewers? How can administrators stop this insanity? Doug Paddock continues to answer these questions and more in this part two of this tutorial on browser elections.



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Doug Paddock

Why do unwanted browser elections keep popping up on Windows administrators' Event Viewers? How can administrators stop this insanity?

I'm answering these questions and more in this two-part tutorial on browser elections. In part one, I offered information on how systems get elected to the various roles used in the Microsoft's Browser Service and explained the roles of domain master browsers and master browsers. In part one's sidebar, I offered a datagram that illustrates the process for initiating a master browser election.

In this, the conclusion of the browser election tutorial, I continue the discussion of how to initiate a master browser election. Then, I describe how to keep one system on a subnet as the subnet's master browser and explain the role of backup browsers.

In the datagram, you can see that the Election Criteria subfield contains two sections, the operating system and election revision. As you can see, WFW or Win9x operating systems are the lowest in the hierarchy, with Windows 2000 and Windows NT 4.0 systems being the highest. If the operating systems are the same, the Election Revision section is used. This is a constant value and deals with the revision of the browser protocol, not the operating system version. If this does not produce a winner, the next criterion is used. A number of items should be considered: being the PDC, being a WINS client, being a Preferred Master Browser, being a Running Master Browser and the total time a server has been running. If nothing else works, the new master browser is chosen alphabetically, starting with A.

When a browser receives an election datagram, it will examine the criteria in the datagram to see whether it has better qualifications to be the master browser than the system that initiated the election. If the receiving system is more qualified to be the master browser, it broadcasts its own election datagram and enters a condition called "election in progress." If the system receiving the election datagram is not more qualified, it will not broadcast anything and will instead try to determine the new master browser's identity.

When a browser thinks that it has won an election, it enters the "running election" state. While it is in this state, it eventually will send out an election request, but it waits first. The wait interval is based upon the browser's current domain role. Master browsers and PDC's wait 100 microseconds (ms). Backup browsers and BDC's (backup domain controllers) wait randomly for 200 to 600 ms. All other browsers wait randomly for 800 to 3000 ms.

The delay is due to Windows for Workgroups systems "blanking out" for several hundred microseconds after sending an election datagram. The wait reduces the total number of election datagrams sent across the network. By having systems least likely to win the election wait longer, the odds are better that they will receive an election datagram with higher criteria than themselves and that they will not broadcast at all.

The browser that believes it has won sends up to four election datagrams. If no other system responds with a higher criteria datagram, this browser is promoted to master browser. If a current master browser is defeated in the election, it will demote itself to a backup browser.

When a new master browser is elected, clients are liable to notice "holes" or missing servers when they browse the network. The holes exist due to the 12-minute gap before all client servers on a subnet register with the new master browser.

That's great, but how do I keep this server as my master browser?

An administrator may want one system on a subnet to be the subnet's master browser for a variety of reasons. If so, an administrator can select a system by editing the HKEY_LOCAL_MACHINE SYSTEMCurrentControlSetServicesBrowser Parameters entry in the registry and setting an entry named "ISDomainMasterBrowser" to "Yes." This entry will let the system in question win all browser elections by giving it priority over all other systems, unless there is a condition that prevents it. For example, the system must be online during an election.

If your Windows 95 systems are forcing elections on the network, you can configure them so that they do not participate in browser elections. The entire procedure is rather lengthy and can be found on Microsoft's TechNet. It is indexed as article Q246489.

If you are running a test lab and your domain controllers are forcing elections when you reboot them (since they have higher criteria than the other systems on the subnet), you can set them so they do not participate in browser elections. In both Windows 2000 and NT 4.0, this value is set under the registry entry:

  • HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesBrowser Parameters
Set this value to "No." This will stop the system from being a browser and cut down on both elections and network traffic.

About backup browsers

Backup browsers are chosen by the master browser on a subnet, and are not elected. As long as:

  • HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesBrowser Parameters
is not set to "No," backup browsers are activated as needed by the master browser. Each subnet typically has one backup browser for every 32 clients. BDC's will typically be backup browsers.

About the author: Douglas Paddock, MCSE, MCT, MCSA, is a CIW Security Analyst who is also who is also A+ and N+ certified. He teaches at Louisville Technical Institute in Louisville, Ky.

FOR MORE INFORMATION:

>> GO BACK TO PART ONE

>> GO BACK TO THE SIDEBAR

>> Check out Douglas Paddock's tutorial about the Microsoft Browser Service

RESOURCES FOR THIS STORY:

>> Chapter 3 - Windows NT Browser Service

>> Appendix I: Windows 2000 Browser Service

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