Installing, Configuring, and Troubleshooting WINS

Windows 2000 now uses DNS as its primary namespace. Pre-Windows 2000 operating systems use NetBIOS names to identify and access computers and resources on a network. To locate computers and resources, NetBIOS names must be registered so they can be mapped to a corresponding IP address. This is where WINS comes into play. Keep in mind that in a pure Windows 2000 network, WINS is not required. However, if there are legacy clients and servers on the network that still use NetBIOS, or applications that require NetBIOS name resolution, WINS may be required.

WINS provides a dynamic database to register NetBIOS names and resolve them to IP addresses. Clients dynamically register their NetBIOS names with a WINS server and query a WINS server when they need to resolve a NetBIOS name to an IP address.

In a non-routed environment, NetBIOS names can be registered and resolved using local broadcasts. However, this poses a problem in a routed environment because routers are not normally configured to forward broadcasts between subnets. WINS solves the problem of registering and resolving NetBIOS names in a routed environment. By using WINS, name registration and renewal requests can be directed to a WINS server, which allows the requests to pass routers, thereby allowing name registration and renewal across subnets.

There are a number of other benefits of implementing a WINS server on a network, including

• It provides a dynamic database for registering NetBIOS names and resolving them to IP addresses.

• It centralizes the management of resolving NetBIOS names to IP addresses and eliminates the need for LMHOSTS files.

• It reduces the amount of broadcast traffic on the network. Clients can directly query the WINS server for name registration and resolution instead of performing a broadcast.

• It allows pre-Windows 2000 clients to locate domain controllers that are not on their local subnet.

LMHOSTS files are another method of resolving NetBIOS names to IP addresses. LMHOSTS files are plain text files that consist of entries mapping NetBIOS names (or computer names) to IP addresses. When a computer needs to resolve a NetBIOS name, it can parse the LMHOSTS file located within the Windows directory. The main disadvantage to using LMHOSTS files is that they must be manually updated.

WINS Resolution

WINS clients communicate with a WINS server in any of the following situations:

• NetBIOS name registration

• NetBIOS name renewal

• NetBIOS name release

• NetBIOS name resolution

NetBIOS Name Registration

When a client is configured to use a WINS server, it registers its NetBIOS name with the WINS server that it has been configured to use. A name registration request is sent directly to the WINS server when the client starts and when any network services, such as the workstation service, is started. The WINS server responds with a successful registration message if another host on the network doesn't already register the same name. The WINS server also returns the Time to Live (TTL), which defines how long the name can remain in the WINS database before it must be renewed (the default TTL is six days).

If the WINS server determines that the name a client is attempting to register is already in the database, the WINS server sends a challenge message to the host that currently has the name registered. If the host responds to the challenge, the host requesting to register the NetBIOS name receives a negative response from the WINS server. If the host that currently uses the name does not respond to the challenge, the WINS server sends a successful registration message, thus permitting the new WINS client to register the name.

There may also be instances when a client attempts to register its NetBIOS name when the primary WINS server is unavailable. In this case, the client will attempt to register its name with a secondary WINS server if it has been configured for one. If no response is received, the client can register the name using a local broadcast. Remember that local broadcasts cannot cross routers, so a name that the machine registers in this way might not be unique.

NetBIOS Name Renewal

As IP addresses leased from a Dynamic Host Configuration Protocol (DHCP) server must periodically be renewed. WINS clients must also renew their registered NetBIOS names with the WINS server by sending a refresh request. The refresh request contains the IP address and NetBIOS name of the requesting client. The renewal process occurs as follows :

1. When half of the TTL is reached, the client sends a name refresh request to the WINS server.

2. If the client receives no response from the primary WINS server, it attempts to renew its name at 10-minute intervals for a total of one hour , at which point it attempts to renew with the secondary WINS server.

3. The client continues to contact the primary and secondary WINS servers until its name is renewed.

4. If the client fails to renew its name before the TTL expires , the client releases its NetBIOS name.

NetBIOS Name Releasing

When a WINS client is properly shut down, it sends a name release request containing its IP address and NetBIOS name to the WINS server. This makes the NetBIOS name available for another client on the network.

NetBIOS Name Resolution

When a client is configured for WINS, it automatically sends any NetBIOS name resolution requests to the WINS server. The WINS server uses its database to map the client to its corresponding IP address. When a client needs to resolve a NetBIOS name, the following process occurs:

1. The client checks its local NetBIOS name cache to see if there is an entry for the remote client.

2. If no entry is present, the request is sent to the primary WINS server.

3. If the primary server fails to respond to the request, the WINS client attempts to resolve the name using one of the other WINS servers it has been configured to use.

4. If none of the WINS servers respond, the WINS client attempts to resolve the name using a broadcast on the local network.

5. If the WINS client does not receive a response, it checks the LMHOSTS file. If no entry exists, the WINS client tries to resolve the name using the HOSTS file, and then contacts a DNS server.