Registration is the process used to register a unique name for each computer (node) on the network. A computer typically registers itself when it starts.
NetBIOS over TCP/IP (NetBT) is the session-layer network service that performs name-to-IP address mapping for name resolution. In Advanced Server, NetBT is implemented through WINS and broadcast name resolution. The two most important aspects of the related naming activities are registration and resolution:
Registration is the process used to register a unique name for each computer (node) on the network. A computer typically registers itself when it starts.
Resolution is the process used to determine the specific address for a computer name.
Note
RFCs 1001 and 1002 specify how NetBIOS should be implemented over TCP/IP and define the name resolution modes.
Defined within NetBT are modes which specify how network resources are identified and accessed. The most common NetBT modes are as follows:
b-node, which uses broadcast messages to resolve names.
p-node, which uses point-to-point communications with a name server to resolve names.
m-node, which first uses b-node and then—if necessary—p-node to resolve names.
h-node, which first uses p-node for name queries and then b-node if the name service is unavailable or if the name is not registered in the database.
Note
The RFCs refer to a NetBIOS Name Server (NBNS). WINS is an enhanced NBNS.
The two most common node types for Windows client computers are h-node and b-node.
For DHCP users, the node type is assigned by the DHCP server. When WINS servers are in place on the network, NetBT resolves names on a client computer by communicating with the WINS server. When WINS servers are not in place, NetBT uses b-node broadcast messages to resolve names. NetBT also can use LMHOSTS files for name resolution, depending on how TCP/IP is configured on a particular computer.
Advanced Server can respond to b-node and h-node NetBT modes. (Windows NT supports all of the NetBT.) Client computers can use the modes described in the following sections.
The b-node mode uses broadcasts for name registration and resolution. That is, if CLIENT_PC1 wants to communicate with CLIENT_PC2, it will broadcast to all machines that it is looking for CLIENT_PC2 and then will wait a specified time for CLIENT_PC2 to respond.
The b-node mode has two major problems:
In a large environment, it loads the network with broadcasts.
Typically, routers do not forward broadcasts, so computers that are on opposite sides of a router will never hear the requests.
The p-node mode addresses the issues that b-node does not solve. In a p-node environment, computers neither create nor respond to broadcasts. All computers register themselves with the WINS server, which is responsible for knowing computer names and addresses and for ensuring no duplicate names exist on the network.
In this environment, when CLIENT_PC1 wants to communicate with CLIENT_PC2, it queries the WINS server for the address of CLIENT_PC2. Upon receipt of the address, it goes directly to CLIENT_PC2 without broadcasting. Because the name queries go directly to the WINS server, p-node avoids loading the network with broadcasts. Because broadcasts are not used and because the address is received directly, computers can span routers.
The most significant problems with the p-node mode are the following:
All computers must be configured to know the address of the WINS server (although this typically is configured using DHCP).
If the WINS server is down, computers that rely on the WINS server to resolve addresses cannot get to any other systems on the network.
The m-node mode was created primarily to solve the problems associated with b-node and p-node. In an m-node environment, a computer first attempts registration and resolution using b-node. If that fails, it switches to p-node.
The advantages of the m-node mode are the following:
The m-node can cross routers.
Because the b-node always is tried first, computers on the same side of a router continue to operate as usual if the WINS server is down.
In theory, it should increase local area network (LAN) performance.
The h-node mode solves the most significant problems associated with broadcast messages and with routed-environment operations. It is a combination of b-node and p-node that uses broadcast messages as a last effort. The h-node mode does more than change the order for using b-node and p-node. If the WINS server is down — making broadcast messages a necessity — the computer continues to poll the WINS server. When the WINS server can be reached again, the system returns to p-node. The h-node also can be configured to use the LMHOSTS file after broadcast name resolution fails.
Because p-node is used first, no broadcast messages are generated if the WINS server is running, and computers can be on opposite sides of routers. If the WINS server is down, b-node is used allowing computers on the same side of a router to continue to operate as usual.
Note
For Microsoft TCP/IP users who configure TCP/IP manually, h-node is used by default unless the user does not specify addresses for WINS servers when configuring TCP/IP.
Another variation, known as modified b-node, is used in Advanced Server networks to allow messages to go across routers. The modified b-node does not use p-node mode or a WINS server. In this mode, b-node uses a list of computers and addresses stored in an LMHOSTS file. If a b-node attempt fails, the system looks in LMHOSTS to find a name and then uses the associated address to cross the router. However, each computer must have this list which creates an administrative burden in maintaining and distributing the list.
Both Windows for Workgroups 3.11 and LAN Manager 2.x use a modified b-node system. Windows NT uses this method if WINS servers are not used on the network. In Windows NT, some extensions have been added to this file to make it easier to manage but modified b-node is not an ideal solution.
Some sites may need to use both b-node and p-node modes at the same site. Although this configuration can work, administrators must exercise caution, using it only for transition situations. Because p-node hosts disregard broadcasts and b-node hosts rely on broadcasts for name resolution, the two hosts potentially can be configured with the same NetBIOS name, leading to unpredictable results. Notice that if a computer configured to use b-node has a static mapping in the WINS database, a computer configured to use p-node cannot use the same computer name.
