How WINS Clients Resolve Names

WINS clients perform NetBIOS name–to–IP address mapping resolution by using the NetBIOS over TCP/IP (NetBT) component. A Windows NT–based computer is automatically configured to use one of four different NetBT name resolution modes (that is, methods for resolving names), based on how TCP/IP is configured on the computer. Table 7.1 describes the NetBIOS modes and how they resolve IP addresses from NetBIOS names.

To display a computer's TCP/IP configuration, including its node type, type ipconfig /all at the command prompt. For example, on a computer that is configured as a WINS client, the node type "Hybrid" appears when you type ipconfig /all .

The name resolution process between an H-node WINS client and a WINS server follows this sequence:

1. When a user types a network-related command at the command prompt, such as net use , the client computer checks its NetBIOS name cache for the NetBIOS name and IP address of the destination host. If the client finds a mapping, the name is resolved without generating network activity.

2. If the client computer does not find the name in the NetBIOS name cache, the client makes three attempts to contact the first WINS server (if one is configured). If the first WINS server does not respond, the client attempts to contact the next WINS server until it has attempted to contact all configured WINS servers. If the name is resolved, the IP address is returned to the client.

3. If the name is not resolved by any WINS server, the client generates three B-node broadcasts on the local network. If the NetBIOS name is found on the local network, the name is resolved to an IP address.

4. If the NetBIOS name cannot be resolved using B-node broadcasts and LMHOSTS lookup is enabled, the client parses the local LMHOSTS file. If the NetBIOS name is in the LMHOSTS file, the name is resolved to an IP address.

5. If the NetBIOS name is not resolved from the LMHOSTS file, the client computer attempts to resolve the name through other host name resolution techniques. If the Enable DNS for Windows Resolution box is checked in the WINS Address property page of the Internet Protocol (TCP/IP) dialog box, it attempts to resolve the name using a local Hosts file or a DNS server.
   To resolve a host name, WINS checks the local Hosts file for a match against the local host name first. If the host name is found in the Hosts file, it is resolved to an IP address. The Hosts file must reside on the local computer.

6. If the name is not resolved from the Hosts file, the client sends a request to its configured DNS server. If the host name is found by a DNS server, it is resolved to an IP address.
   If none of these methods resolve the NetBIOS name, the net use command returns an error, indicating that the computer could not be found.

Figure 7.4 Name Resolution via WINS

In Figure 7.4, the initial message is the name request from the client to its primary WINS server. This is followed by the response from the WINS server, returning the desired IP address. Once the response is received, the client uses this address to establish a connection to the desired resource.