WINS Database

When a client is turned off, it releases its name, but there is a WINS extinction interval that allows the record to remain for some period of time in case the client is turned on again (as in the case of a reboot). The extinction interval reservs the record for some period so other clients cannot use it until the interval expires. WINS files are in SystemRoot\System32\Wins. A file names WINS.MDB is used to store a WINS database which can be backed up and repaired. The WINS service will back up the database every three hours (by default) to the configured backup path. Version numbers can be used to backup minor changes. The only way to replace a new copy with an older copy is to delete the old database copy first. The easy way to restore a database is to force replication from a WINS partner with a good copy of the database.

The database contains the following records:

• Renewal interval - Equivalent to the DHCP lease interval, it is the amount of time for the client to re-register the NetBIOS name before it is released.
• Extinction interval - The time a releast record exists before being tombstoned.
• Extinction timeout - The time a tombstoned record exists before being erased.
• Verification interval - The time an active record exists before being verified with the name owner.

WINS Proxy Agent

A WINS proxy agent can be configured to act as a relay for non-WINS clients. The WINS proxy agent can intercept client broadcast requests, forward them to a WINS server and return the response. It may also reply with the response without contacting the WINS server if the required information is in its cache. One WINS proxy is used on each subnet that has non-WINS clients. This means that machines that are not using WINS (Even Windows machines such as those without TCP/IP) can use a proxy agent to let them find resources on other subnets. There should be a maximum of two proxy agents per subnet. The agent must be a Windows based client, not a server. When NetBIOSs names are registered, both the proxy agent and the WINS server checks the name. The proxy agent is configured at the following registry location:

Hkey_Local_Machine\System\CurrentControlSet\Services\NetBT\Parameters

Set the EnableProxy parameter to REG_DWORD value of 1 and restart the computer.

WINS Operation

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:
1. Local cache
2. WINS server (primary then secondary, two times).
3. Broadcast
4. Lmhosts file
5. Hosts file
6. DNS