Windows Networking Concepts

The following definitions explain some common Windows networking terms:

B-Node
(Broadcast node)

Type of NetBIOS end node that supports NetBIOS service and contains applications. B-nodes communicate using a mix of UDP datagrams and TCP connections. B-nodes can freely interoperate with one another within a broadcast area; normally a single LAN segment. Other standard end nodes are point-to-point nodes (P-nodes) and mixed-mode nodes (M-nodes).

Browsing

Viewing the resources available on a network. The browse list on a Windows network is the list of other hosts and domains available on a network. Windows maintains the browse list to present other hosts offering network services through a point-and-click user interface rather than asking users to remember the names of remote hosts and services. Windows clients use the browse list to construct the view of the network shown in the Network Neighborhood (renamed My Network Places in Windows 2000) and Windows Explorer. The browse list is also accessible from the command line using the NET VIEW command.

Windows for Workgroups and Windows NT domains maintain the browse list on a computer called the Master Browser. Whenever a computer offers a network service for the first time, it broadcasts a server announcement packet. The Master Browser receives this packet and adds the computer's name to its browse list. In response, the Master Browser transmits a list of backup browsers to the new computer.

Each domain or NT group contains at least one backup browser. A copy of the browse list is maintained on the backup browser to eliminate the need to rebuild the browse list if the Master Browser goes down. For more information about NT domains and network browsing, see the related Microsoft technet site on the World Wide Web.

CIFS

Common Internet File System protocol. CIFS provides an open cross-platform mechanism for client systems to request file services from server systems over a network. It is based on the SMB protocol widely used by PCs and workstations running a wide variety of operating systems.

NetBIOS

NetBIOS, or Network Basic Input/Output System, is a vendor-independent network interface originally designed for IBM PC computer systems running PC-DOS or MS-DOS. NetBIOS is a software interface, not an actual networking protocol. It specifies the services that should be available without putting any restrictions on the protocol used to implement those services.

No officially defined NetBIOS standard exists. The original version, as described by IBM in 1984 in the IBM PC Network Technical Reference Manual, is treated as the de facto standard. Since its introduction, the following versions of NetBIOS have emerged, each using its own transport protocol: NetBEUI, NetBIOS over IPX, and NetBIOS over TCP/IP.

AIX Fast Connect uses NetBIOS over TCP/IP.

NetBIOS Interface to Application Programs

On PCs, NetBIOS includes both a set of services and an exact program interface to those services. The following types of NetBIOS services exist:

Name Service

NetBIOS resources are referenced by name. Lower-level addresses are not available to NetBIOS applications. An application representing a resource registers one or more names that it wants to use.

The name space is flat and not hierarchically organized. It uses 15 alphanumeric characters, plus a 16th "subcode" byte. Names cannot start with an asterisk (*).

Registration implies bidding for use of a name. The bid may be for exclusive (unique) or shared (group) ownership. Each application contends with other applications in real time. No two applications on the NetBIOS network can use the same unique name until the originating application requests that its name be deleted or the host is powered off or reset.

Name Service provides the Add Name, Add Group Name, and Delete Name primitive operations.

Session Service

A session is a full-duplex, sequenced, and reliable message exchange conducted between a pair of NetBIOS applications. Data is organized into messages.

Multiple sessions can exist between any two applications. Both applications participating in the session have access to the name of the remote application. No specification is given for resolving session requests to a group name into a data connection. A service is provided for the detection of a session failure by an application.

The Session Service provides the Call, Listen, Hang Up, Send, Receive, and Session Status primitive operations.

Datagram Service

The Datagram Service is an unreliable, nonsequenced, and connectionless communication between two NetBIOS applications. It is analogous to UDP service under TCP/IP.

Datagrams are sent under cover of a name properly registered to the sender. Datagrams can be sent to a specific name or be explicitly broadcast.

Datagrams sent to an exclusive name are received, if at all, by the holder of that name. Datagrams sent to a group name are multicast to all holders of that name. The sending application cannot distinguish between group and unique names and thus must act as if all nonbroadcast datagrams are multicast.

As with the Session Service, the receiver of the datagram is provided with the sending and receiving names.

The Datagram Service provides the Send Datagram, Send Broadcast Datagram, Receive Datagram, and Receive Broadcast Datagram primitive operations.

NetBIOS Name Resolution

Mapping a NetBIOS name to its corresponding IP address. The techniques commonly used for name resolution are the Windows Internet Name Service (WINS), the LMHOSTS file, and the domain name system (DNS). For information about DNS, see NetBIOS Name Resolution. The other techniques are defined as follows:

WINS/NBNS

When a new service is made available on the network, such as when a Windows machine boots or when AIX Fast Connect is started, the service must be registered with a WINS server before it can be available to clients located on other subnets. The WINS server records the name of the host, the NT domain the host is part of, and the IP address of the host. Whenever a machine attempts to resolve a host name, it first checks with the WINS server. If the host is not registered there, it attempts to find the host using a broadcast. If the host is still not found, the system returns the messageA computer or sharename could not be found. AIX Fast Connect registers itself with any WINS server.

WINS also includes a method for replicating its database of host names with other WINS servers to create a backup WINS server that can host queries if the primary WINS server is unavailable. It also allows large networks that are encumbered by slow links to distribute WINS servers closer to clients and provide faster name resolution. (WINS is a proprietary Microsoft protocol.)

AIX Fast Connect can be configured to act as an NBNS (NetBIOS Name Service) server, providing most WINS functionality. AIX Fast Connect can also be configured to act as a WINS proxy to other WINS or NBNS servers. For details, see NetBIOS Name Service (NBNS).

LMHOSTS

LMHOSTS (LanManager Hosts) is analogous to the UNIX /etc/hosts file. The LMHOSTS file allows specific NetBIOS server names to be mapped to IP addresses. It also provides a syntax for defining the domain in which a NetBIOS server resides, as well as loading an LMHOSTS file from a shared directory on a server.

NetBIOS over TCP/IP

NetBIOS over TCP/IP was first proposed in RFCs 1001 and 1002. These RFCs describe an implementation of NetBIOS using Transmission Control Protocol (TCP) for connection-oriented session services and User Datagram Protocol (UDP) for datagram services.

This design has some significant advantages over NetBEUI and NetBIOS over IPX, as follows:

• NetBIOS uses the existing TCP/IP protocols, so it can be routed across the global Internet and any other wide area networks.
• Software implementing the NetBIOS interface can be built using existing TCP/IP implementation without requiring any new network drivers. Because most operating systems already support TCP/IP, most are capable of supporting NetBIOS with minimal additional effort.

NetBIOS Scope

Population of computers across which a registered NetBIOS name is known. NetBIOS broadcast and multicast datagram operations must reach the entire extent of the NetBIOS scope.

net Command

The net command and its subcommands can be used to configure and administer the AIX Fast Connect Server from the command line. Alternatively, the Web-based System Manager and SMIT offer menu-driven interfaces for the same tasks. For detailed information, see net Command.

Passthrough Authentication

Mechanism employed by the AIX Fast Connect server to validate user credentials with a domain controller and, if validated, to grant the user access to a resource on the AIX Fast Connect server.

SMB

Server Message Block protocol used to run on NetBIOS to implement Windows file sharing and print services.

With this protocol, clients exchange messages (called server message blocks) with a server to access resources on that server. Every SMB message has a common format, consisting of a fixed-sized header followed by a variable-sized parameter and data component.

SMB messages are of the following types:

• Session control messages start, authenticate, and terminate sessions.
• File and printer messages control file and printer access, respectively.
• Message commands allow an application to send or receive messages to or from another host.

When an SMB client negotiates a connection with an SMB server, the two parties determine a common protocol to use for communication. This capability allows protocol extensions but can make SMB quite complex.

Shares

Resources exported to the network by the AIX Fast Connect server. AIX Fast Connect supports AIX file shares and printer shares.

Workgroups

Logical collection of workstations and servers that do not belong to a domain. In a workgroup, each computer stores its own copy of user- and group-account information. Therefore, in workgroups, users can only log directly in to machines on which they have accounts. Workgroup members are able to view and use resources on other systems. To do this, resources are shared in the workgroup and network users are validated by the machine owning the resource.