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This article discusses how resource browsing works across a Wide Area Network (WAN) and how Microsoft's Windows Internet Name Service (WINS) improves cross-subnet browsing.
Browsing with Windows NT version 3.1 (pre-WINS)In Windows NT version 3.1, browser information transmission relies almost entirely on network broadcasts. In a WAN environment (using a network protocol such as TCP\IP) domains are typically separated by routers. To reduce bandwidth usage, broadcast packets are often filtered and do not pass through routers thus limiting them to the local subnet.
As a result, the Windows NT version 3.1 default B-Node name resolution cannot resolve names on remote subnets. Each local subnet functions as an independent browsing entity, with its own Master Browser and Backup Browsers. Browse elections occur on a per subnet basis.
Windows NT Advanced Server version 3.1 supports cross-subnet browsing. To browse across a WAN, at least one Windows NT Advanced Server is required in each subnet. The Domain Master Browser is responsible for maintaining a WAN wide browse list of available servers in the domain and all accessible domains.
When a domain spans multiple subnets, the Master Browsers for each subnet announce themselves to the Domain Master Browser using the directed datagram, "MasterBrowserAnnouncement". The Domain Master Browser then remotes a "NetServerEnum" call to the Master Browser that announced itself in order to collect that subnet's list of servers. The Domain Master Browser merges the server list from the Master Browser with its own server list. This process is done every 15 minutes to guarantee that the Domain Master Browser has a complete list of servers in the domain.
Now, when a client remotes a "NetServerEnum" call to the Master Browser, the Master Browser will be able to return all of the servers in the domain, regardless of what subnet they are on.
NOTE: A Windows NT workgroup cannot span multiple subnets. If a Windows NT workgroup is implemented across two or more subnets, it will function as separate workgroups.
To ensure each subnet's Master Browser can access every domain's Primary Domain Controller (PDC), the Master Browser must maintain a LMHOSTS file containing the name of each domain's PDC and Backup Domain Controllers (BDC) with a #DOM extension. To guarantee that each PDC can access the local browse list from each subnet's Master Browser, TCP/IP (and other WAN protocols) must cache the client address for a reasonable period of time.
Browsing with Windows NT Server version 3.5 or later with WINSWindows NT Server versions 3.5 or later include the Windows Internet Name Service (WINS). WINS is basically a directory service for NetBIOS names and IP addresses.
The Domain Master Browser registers a unique Browser name of "<DOMAIN>[1B]" with the WINS server. Other Domain Master Browsers will periodically query the WINS server for a list of domains. They then merge this list into their local domain browse list. They then propagate this list to the Master Browser on each subnet via the mechanism mentioned above.
The Domain Master Browser queries the WINS server in a two part process:
NOTE: Only WINS-aware Domain Master Browsers (those in Windows NT versions 3.5 or later) will register their <DOMAIN>[1B] name with the WINS server. Windows NT version 3.1 Domain Master Browsers will not use WINS.
Windows NT Workstation versions 3.5 or later are WINS-AwareWindows NT Workstation versions 3.5 or later remote the "NetServerEnum" call to a Backup Browser Master for its domain. The list of domains returned includes those the Domain Master Browser discovered via the WINS server. When the Workstation browses a remote domain it will query the WINS server for the IP address of the computer that registered the <DOMAIN>[1b] name. The Workstation then sends a "GetBackupListReq" to the IP address and picks one of the machine names from the response and remotes a "NetServerEnum" call to that name to get a list of computers in that domain.
Windows NT version 3.1 Clients are Not WINS-AwareWhen the Windows NT 3.1 client browses a remote domain, it sends a "GetBackupListReq" to the name <DOMAIN>[1d], not <DOMAIN>[1b]. Because there is no Domain Master Browser for this domain in its subnet. The client will eventually give up and will perform a "double hop" to its local Domain Browser Master. The browser server will remote the NetServerEnum API for the client. How the remote is resolved depends on if the browser server is WINS aware or not.
Windows for Workgroups version 3.11 Clients with TCP/IP-32 are WINS-AwareWindows for Workgroups version 3.11 clients can be WINS aware through TCP/IP-32 for Windows for Workgroups. WINS will help with standard workstation connections. However, the browser code that they use is not WINS or WAN aware. If the Windows for Workgroups client is in local browser domain that has a Windows NT 3.5 or later browser server, the client will see a list of all remote domains. However, if the client selects one of these names it will not be able to resolve it. The client is unaware of the special [1b] name.
Article ID: 120151 - Last Review: February 28, 2014 - Revision: 2.2