Sams Teach Yourself MCSE Windows NT Server 4 in 14 Days
(Publisher: Macmillan Computer Publishing)
Author(s): David Schaer, et al
ISBN: 0672311283
Publication Date: 12/15/97

If more than one IP address is configured for the host, then the amount of space increases proportionately to the number of IP addresses. In addition, if the registered name is a group name such as domain name (1C), the record can be up to 480 bytes if it contains the maximum number of registered hosts.

During replication, the amount of network traffic depends on the number of records to be transferred, which will vary for each session. In addition, the number of records to be transferred may be different for each session.

Each entry is about 50 bytes. When replication occurs, these entries are combined to create the smallest number of packets. The replication traffic consists of session establishment and WINS control frames as well as the frames containing the data.

Name Registration

After initialization of TCP/IP, the host then registers its NetBIOS names. This can be done either through b-node broadcasts or by sending the registration to a NetBIOS name server such as WINS.

All services and applications that use NetBIOS must be registered. The number of names a host registers is variable and reflects network services and applications that the host initializes. These include the computer’s role—PDC, the Workstation and Server services, or NetBIOS applications such as Network Monitor. Each host registers an average of three or four names.

Each NetBIOS name is 16 characters long with the 16th character reserved as a designator of the service or application that owns the name. The configurable portion of the NetBIOS name can be up to 15 characters long, and can be something like the computer’s name. If this portion of the name is less than 15 characters, then the name will be padded to a length of 15 characters.

The registration of each name generates a packet 214 bytes long and takes less than 100 milliseconds to complete the registration process. Figure 11.19 shows the registration process using Network Monitor.

Figure 11.19.  Network Monitor showing WINS registration.

WINS Name Renewal

After a name is registered, the WINS server sends a success message that assigns a Time to Live (TTL) to that name. The TTL is used to determine when the host must renew that name. The default TTL is 144 hours, or 518,400 seconds.

Each host renews its names when half of its TTL has elapsed, or every three days with the default configuration. After a successful renewal, the TTL for the host’s names is reset to the original length. The length of the TTL determines how much traffic will be generated for name renewals.

Name Resolution

NetBIOS names enable us to use friendly names to access various resources on the network. To find the resource we need, however, a method must be in place to ensure that no two resources use identical names.

WINS resolves NetBIOS names to IP addresses to provide a way to locate these resources. When a host wants to locate a resource it sends a name query request to the WINS server containing the name to be resolved and a query flag. The WINS server responds with a name query response packet if that name is registered. This packet contains the IP address of the registered owner of the resource.

Name resolution involves only two packets. The host sends a name query request and the WINS responds with a name query response containing either the IP address of the name’s owner or a “Requested name does not exist” message. These two frames are less than 200 bytes in size and can take only a couple of milliseconds if network traffic is light.

If the name is not registered with WINS, the client assumes that the name’s owner is not a WINS client and resorts to broadcasting to resolve the name if configured to do so.

Note in Figure 11.20 the two frame conversation resulting in a Requested name doesn’t exist message (frames 1378 and 1379). The host then sends a broadcast message to locate the name’s owner.

Name Release

When a host shuts down or stops a service, it sends a release request to the WINS server. This release is the same size as a registration (110 bytes) and the WINS responds with a success message (104 bytes) which sets the TTL to zero. After a name is released, another host can register it. When a computer shuts down, two frames are sent for each registered name.

Figure 11.20.  Network Monitor showing failure of WINS name resolution.

Managing Static Mappings in WINS

One of the strongest features of WINS is that it dynamically keeps up with NetBIOS names and IP addresses, and little manual configuration is required. Non-WINS clients, however, cannot participate in this in the normal way.

When a client that cannot use WINS initializes itself, it does not register its NetBIOS name with the WINS server. For WINS clients to be able to locate non-WINS clients, you must configure static mappings. This entails manually entering the NetBIOS name and IP address for a computer into the WINS database. You do this in the following manner:

1.  In WINS Manager, choose Static Mappings from the Mappings menu. This brings up the Static Mappings dialog box shown in Figure 11.21.

Figure 11.21.  Editing static mappings using WINS Manager.

2.  Choose the Add Mappings button to bring up the Add Static Mappings dialog box (see Figure 11.22).

Figure 11.22.  Adding a static mapping to the WINS database.

3.  Enter the NetBIOS name and IP address of the client computer. You also can choose the type of client you are mapping. These types are described in Table 11.1.