Name Management

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Name Management

When a system is going to communicate with another computer on the network, some method of identifying the other computer is required. The identification is, of course, handled in the NetBIOS world by the computer name (which can be up to 15 characters in length). When IBM and Microsoft developed the NetBIOS standard, fewer wide area networks (WANs) existed, and generally the local area networks (LANs) were small enough that they did not require the capability to be segmented.

Generally, main frame and mini-computers were used when segmenting was required. Looking at other networking technologies, such as TCP/IP, that required computers to have numeric addresses, Microsoft and IBM decided that NetBIOS should use computer names to put a friendly face on the network because these could be resolved using broadcasts.

Because the identity of the system is the name, each name that you use for a computer must be unique on the network. However, as time has passed, networks became larger and it became desirable to group computers on the network and to be able to send information (messages) to users working on the computers. This lead to the requirement for multiple NetBIOS names. Currently, Windows NT enables you to register up to 250 NetBIOS names for any given computer. The common names that Windows NT registers are as follows:

Computer name. This is the name that the computer uses on the network,; in all cases, this name must be unique. When a system starts and the name is already on the network, the networking portion of the system cannot initialize. (It is possible to duplicate a name in some multi-segment networks; however, the hosts can never communicate. This is because the name is checked on the local segment or on a NetBIOS Name Server).
User name. The user name also is registered on the network. This enables the user to receive messages (such as printer notifications) that are sent to the user name. More than one instance of a user name can exist. However, only the first person to register the name receives messages; all other attempts to register that name fail until the person currently using the name shuts down. (The system continues to function correctly, but the user does not receive any messages.)
Workgroup or domain name. This is a group name, and many different systems can register the name. This name is used to group computers into a single management area (a set of computers that are managed together).

Being as there are several different types of names, you may have more than one name registered on your computer. This is further complicated by the need to find a service that is running on a computer (for example, if you are trying to access network resources, the Workstation service in your system needs to communicate with the Server service on the remote system). If you think about sending a letter, simply addressing the letter to an apartment building does not get it to the person to whom you are writing. In the same way, sending an SMB to a computer does not guarantee that it reaches the correct service on the computer. Many services can use NetBIOS. The three most common services in Windows NT are as follows:

Server Service. Provides the resources of your system for the other computers on the network to use
Workstation Service. Enables you to use the services of another computer that is running the Server Service
Messenger Service. Receives and displays messages for the names that are registered on your computer

As you can see, getting the information to the computer is half the battle. To make the network function, you need to connect to the correct service (end point). This means you require not only the name of the computer, but also the name that the service registered.

Thankfully, this is easy. When I noted previously that the names are 15 characters, I was referring to the portion you can enter. NetBIOS names are, in fact, 16 characters long; the last character identifies the service. Each service adds a 1-byte identifier to the end of the name when it is registered. The following is a list of some of the names that are registered and the services that they represent. (Note that the number the service uses is given in hexadecimal format—it is hard to see a space or a null in print.)

Computername[0x00].
The Workstation service on the computer being registered.
Computername[0x03].
The Messenger service registering on the computer.
Username[0x03].
The Messenger service registering the logged-on user on the network.
Computername[0x20].
The Server service registering the computer on the network.
Domainname[0x00].
Registers the computer as a member of the domain (or workgroup, as the case may be).
Domainname[0x1E].
Facilitates browser elections (also used in workgroup environments—browsing is covered in Chapter 10, “IP Internetwork Browsing and Domain Functions”).
Domainname[0x1B].
Registers the computer as the Domain Master browser (covered in Chapter 9, “Administering a WINS Environment”).
Domainname[0x1C].
Registers the computer as a domain controller, which enables your system to find a domain controller for logon validation.
Domainname[0x1d].
Registers the system as the local subnet’s Master Browser.

Suppose, for example, that you are on a computer called WKS2399 and want to retrieve a file called exprep.xls from a server on a network called NTS94. In this case, an SMB is created by the application layer with a request to get the file, and your workstation service uses the NCB to get to a computer called NTS94[0x20]. After the server receives the SMB and wants to send the information back, it sends it to WKS2399[0x00].

Obviously, your system must have some way to find the server—that is, to resolve the name from NTS94[0x20] to a MAC address where it can send the information.

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