Example of WINS Lookup

Suppose a user at a client workstation issues the following command:

net use \\host-a.noam.reskit.com.\public

This command establishes a connection between the client workstation and the Public folder on the computer host - a.noam.reskit.com, which is a client that is running Windows NT 4.0. However, before the connection can be established, the FQDN host - a.noam.reskit.com must be resolved by DNS — or, in this case, WINS — to an IP address. Figure 6.23 shows how this name is resolved, assuming that no server has cached the data and that no server is forwarding queries.

Figure 6.23 Example of WINS Lookup

1. The client queries its preferred DNS server.

2. DNS servers carry out the normal process of recursion as the preferred DNS server queries other DNS servers in succession on behalf of the client. This process concludes at Step 8, when the DNS server for the noam.reskit.com zone is located through the previous chain of referral answers. At this point in the process, the server that is contacted is a Windows DNS server that is running either Windows NT Server 4.0 or Windows 2000 Server.
   When the Windows DNS server authoritative for the noam.reskit.com zone receives the query for "host - a," it looks in its configured zone to see whether a matching A resource record can be found. If no A resource record is found and the zone is configured to use WINS lookup, the server does the following:

3. The DNS server separates the host part of the name (host - a) from the FQDN contained in the DNS query.
   The host part of the name is the first label.

4. The server then sends a NetBIOS name request to the WINS server using the host name host - a.

5. If the WINS server can resolve the name, it returns the IP address to the DNS server.

6. The Windows DNS server then returns this IP address information to the original preferred DNS server that was queried by the requesting client.

7. The preferred DNS server then passes the query answer back to the requesting client.

The client workstation establishes the session with host - a.noam.reskit.com and connects to the public folder.

In this example, only the last name server in the referral chain had knowledge of WINS. To the client resolver and all other name servers, it appears that DNS was responsible for the entire name resolution process. Furthermore, if the IP address changes for host - a.noam.reskit.com, WINS automatically handles it. Nothing needs to change with DNS.

A reverse lookup with WINS integration works a little differently than the previous example. Because the WINS database is not indexed by IP address, the DNS server cannot send a reverse name lookup to a WINS server to get the name of a computer given its IP address. The DNS server instead sends a node adapter status request directly to the IP address implied in the DNS reverse query. When the DNS server gets the NetBIOS name from the node status response, it appends the DNS domain name specified in the WINS - R record to the NetBIOS name provided in the node status response and forwards the result to the requesting client.