Information on Browser Operation

• Microsoft Windows NT operating system version 3.1
• Microsoft Windows NT Advanced Server version 3.1
• Microsoft Windows NT Workstation versions 3.5, 3.51, and 4.0
• Microsoft Windows NT Server versions 3.5, 3.51, and 4.0

SUMMARY

The Computer Browser service lets you track servers that are active on the network with a minimum of network overhead. It consists of two components on a Windows NT or Windows NT Advanced Server computer.

The User Mode component is the Browser, which is part of the LAN Manager Server service. This portion is responsible for maintaining the browse list, remoting the NetServerEnum API, and managing the computer's role as a Browser (or non-Browser).

The Kernel Mode component is the Datagram Receiver and is in charge of receiving and managing datagrams.

Browser Roles

A network can contain the following types of servers related to browsing:

Non-Browser Servers - Do not maintain browse lists, but announce themselves periodically to the Master Browser.

Potential Browser - Can become a Browser server if needed.

Backup Browser - Maintains a browse list of servers and domains that it retrieves from the Master Browser.

Master Browser - Receives server and Domain announcements, sends browse lists to Backup Browsers, responds to clients requesting browse server lists, promotes Potential Browsers to Backup when needed, and announces the domain to inform the Master Browsers of other domains of the domain name and Master Browser for that domain.

Preferred Master Browser - Same as Backup Browser except that it is biased in elections through setting the IsDomainMasterBrowser to TRUE is the registry's browser parameters.

Domain Master Browser - The primary domain controller of a domain is given a special bias in browser elections so that it will become the Domain Master Browser. This allows browsing to be effective when a domain spans multiple subnets. A directed datagram is used by Master Browsers on each subnet to announce itself to the Domain Master Browser. This is made possible through an entry in the LMHOSTS file on the Master Browsers for the Domain Controller. This makes it necessary to have a Windows NT Advanced Server computer to browse across wide area network (WAN) connections.

There will be at least one Master Browser on a workgroup/domain and one Backup Browser for every 32 systems in that workgroup/domain. This means that in a domain/workgroup with fewer than 32 systems, there will be one Master and one Backup Browser. One more Backup Browser will be added for every 32 systems. This is accomplished by the Master Browser telling a Potential Browser to become a Backup Browser.

Browser NetBIOS Names

Several special NetBIOS names and Mailslots are used to maintain and retrieve browse lists. Names listed here as "DOMAIN(xx)" indicate the domain name followed by the hex value (xx) and padded with spaces to the 16th byte.

<01><02>__MSBROWSE__<02><01>

This name is registered by the Master Browser and is used to broadcast and receive domain announcements on the local subnet. It is through this name that Master Browsers for different domains learn the names of different domains and the names of the Master Browsers on those domains.

DOMAIN(00)

This is the name to which server announcements are broadcast in Microsoft LAN Manager so that other Microsoft LAN Manager computers can track the servers on the network. Windows NT computers do not make these broadcasts unless the LMAnnounce option has been enabled by configuring the Server service with the Control Panel/Networks application. This means that LAN Manager systems will not see these computers unless this option is enabled.

A LAN Manager server within the Windows NT domain will be seen by the Browser and therefore other systems on the network. A LAN Manager domain that doesn't contain any Windows NT computers will not appear on the browse lists unless it is specified as an Other Domain through the Control Panel/Networks application in the Computer Browser configuration.

DOMAIN(1D)

This name is registered by Master Browsers. It is used by clients to find a Master Browser server. A client will broadcast to this name to get a list of browser servers from the Master Browser. The Master Browser will send a list of browser servers to the client from which the client will cache three of these server names. The client will then randomly pick one of these servers to request a list of servers and domains from.

DOMAIN(1B)

This name is registered by the primary domain controller in a domain only and allows unique identification of that computer.

DOMAIN(1E)

This name is registered by all Browser servers and Potential Browser servers in a domain or workgroup. It is used for announcement requests which are sent by Master Browsers to fill up its browse lists, and for election request packets to force an election. Elections are performed by sending a packet out to this name that contains your election criteria.

The election criteria for a Browser is based on the Browser's current role in the domain and its current state, using the following hierarchy:

   Operating System Type:        0xFF000000
   Windows for Workgroups:       0x00000000
   Windows NT:                   0x01000000
   Windows NT Advanced Server:   0x02000000
   Election Version:             0x00FFFF00
   Per version criteria:         0x000000FF
   PDC:                          0x00000080
   Preferred Master:             0x00000008
   Running Master:               0x00000004
   MaintainServerList = Yes:     0x00000002
   Running Backup Browser:       0x00000001

The criteria for determining if a Browser has won an election is the following:

• If your election version is greater than the sender's election version, you win.
• Else if your election criteria is greater than the sender's criteria, you win.
• Else if you have been up longer than the sender, you win.
• If the above comparisons fail to determine a Master Browser, the computer with the lexically lowest name will win the election.

Mail Slots

Server and Domain Names in the browse list are aged and are removed from the browse list if they have not been heard from in three Announce periods.

The Browser uses Mailslot Transactions to pass these messages between systems. Two Mailslots are used.

For messages intended for all systems including LAN Manager and Windows for Workgroups, MAILSLOT\LANMAN is used.

MAILSLOT\BROWSE is used for messages intended for Windows NT and Windows NT Advanced Server systems.