When a NetBIOS broadcast is to go out, a computer sends over TCP/IP to a WINS server to resolve NetBIOS names. WINS dynamically builds its database. When a client uses WINS it announces to the WINS server over TCP/IP rather than broadcasting to all computers. WINS Message Modes:
- Client Name Registration - When a client service is started, the appropriate NetBIOS name for that service, for all NetBIOS processes (Using the hidden 16th byte) is sent to the WINS server. If the registration fails, the client retries every ten minutes. If the primary WINS server fails to respond, the request is sent to the secondary WINS server after three tries. If no WINS server responds, B-node broadcasts are used by the client. When contacted, the WINS server returns a time to live (TTL) field containing the length of time the client may use that name. If a duplicate name is received, the server sends a wait for acknowledgement (WACK) to the registering client. Then a challenge is sent by the server to the registered client. If the current owner responds correctly, the new client request is rejected.
- Client Lease Renewal - When the name lease is at 50%, the client sends a name renewal request to the WINS server with its name and IP address. When the lease is 7/8 up, the client will try again then attempt a lease with the secondary WINS server. After 4 attempts with the secondary WINS server, it attempts lease renewal with the primary WINS server again.
- Client Name Release - The client sends a name release message with its name and IP address. The server responds with a positive release message. If no confirmation is received by the client a NetBIOS broadcast release is sent up to three times.
- Server Name Query and Name Resolution response - With WINS server on the network, resolution is done using H-node on UDP port 137 (NetBIOS Name Service). Name query order:
- Local cache
- WINS server (primary then secondary, two times).
- Broadcast
- Lmhosts file
- Hosts file
- DNS
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