What is NetBIOS and how does it work?

In the complex world of computer networks, it facilitates communication by playing an important role. Widely used in Windows operating systems, this API allows devices on the network to recognise each other and share data. By acting as a bridge between IP addresses and computer names, it forms the basis for network security and efficient communication.

In this article, we will take an in-depth look at what NetBIOS is and how it works. First, we will look at the definition and historical development of NetBIOS. Next, we will discuss its basic components and explain the name resolution process. Finally, we will evaluate the importance of NetBIOS in today’s network environments and its relationship with TCP/IP. This journey will help you fully understand the role of NetBIOS in network communications, covering concepts such as domain controllers and WINS.

Definition and History of NetBIOS

What is NetBIOS?

NetBIOS stands for Network Basic Input/Output System. This system is an API that allows different computers on a local area network (LAN) to communicate with each other. Although NetBIOS is generally known as a protocol, it is actually an API that provides communication over protocols. This API allows devices on the network to perform basic functions such as data sharing and transfer.

NetBIOS names consist of 16 ASCII characters and are single part. However, Microsoft has limited this name to 15 characters and reserved the 16th character as NetBIOS suffix. This structure is used especially in small networks and is generally preferred in internal networks.

Development process of NetBIOS

NetBIOS dates back to 1983. This system, developed by Sytek Inc. for IBM, was originally designed for PC-Network. The first version could only support up to 80 devices. Over time, NetBIOS’s API became a de facto standard.

In 1985, IBM implemented the token ring networking scheme and a NetBIOS emulator was produced so that NetBIOS applications could run on this new design. In 1986, with Novell’s release of Advanced Novell NetWare 2.0, NetBIOS was encapsulated in the IPX/SPX protocol.

With the introduction of the PS/2 computer in 1987, IBM released the PC LAN Support Programme. This programme included a driver for NetBIOS. At the same time, a method of encapsulating NetBIOS in a TCP packet was developed and NetBIOS over TCP/IP standards were established.

Current use of NetBIOS

Today, NetBIOS mostly works over the TCP/IP protocol. This is referred to as NetBIOS over TCP/IP. This structure allows legacy NetBIOS-based applications to be used in modern TCP/IP networks.

NetBIOS provides three basic services:

1. Name service for name registration and resolution
2. Data unit distribution service for connectionless communication
3. Session service for connection-based communication

However, the use of NetBIOS names is limited today. The reason for this is that 15-character names are no longer sufficient and larger structures are needed, especially in the Internet environment. This situation has made the computer world DNS-based instead of NetBIOS. Nevertheless, some applications still use NetBIOS and when configured correctly, it allows these applications to run on large TCP/IP networks.

Basic Components of NetBIOS

NetBIOS consists of three basic components: Name Service, Session Service and Datagram Service. These components provide communication and data sharing of devices on the network.

Name Service

The Name Service provides a mechanism for registering and resolving NetBIOS names. NetBIOS names are endpoint addresses that represent an application or service running on a node on the network. This service uses UDP/137 and TCP/137 ports.

NetBIOS names consist of 16 ASCII characters and are one part. Microsoft has limited this name to 15 characters and reserved the 16th character as NetBIOS suffix. This structure is especially preferred in small networks and in-house networks.

WINS (Windows Internet Name Service) is a method used for NetBIOS name resolution. WINS registers and queries dynamic mappings of NetBIOS names of computers and groups on the network. This service is designed to solve problems that arise during NetBIOS name resolution in routed environments.

Session Service

The Session Service provides reliable, point-to-point communication. This service uses port TCP/139. The CIFS (Common Internet File System) protocol, when using the NetBIOS session service, makes no attempt at a higher level to ensure reliable and sequential transmission of messages. The underlying transport layer is responsible for detecting failures of the client or server node and transmitting error notifications.

The Session Service controls connections between devices. It can establish, manage and terminate local and remote connections. It is also responsible for messaging rules, controlling messaging between applications, and grouping data to go to different units.

Datagram Service

The Datagram Service provides a connectionless and unreliable transport service. This service uses the UDP/138 port and is used for single broadcast, multicast and broadcast messages (datagrams).

Since the data unit mode is ‘connectionless’, NetBIOS data units are sent over UDP. If a data unit is sent to a specific NetBIOS name, it is transmitted with a ‘Direct Unique’ or ‘Direct Group’ packet. If it is sent to all NetBIOS names in the network, a ‘Broadcast’ packet is used.

These three basic components allow NetBIOS to provide effective communication and data sharing between devices on the network. However, the use of NetBIOS names is limited today. The reason for this is that 15-character names are insufficient and larger structures are needed, especially in the Internet environment. This situation has made the computer world DNS-based instead of NetBIOS.

NetBIOS Name Resolution Process

The NetBIOS name resolution process is vital for computers to recognise and communicate with each other on local networks. This process allows NetBIOS names to be mapped to IP addresses.

NetBIOS naming conventions

NetBIOS names consist of 16 ASCII characters and are one part. Microsoft has limited this name to 15 characters and reserved the 16th character as a NetBIOS suffix. Names can contain a period but cannot begin with a period. Some special characters (backslash, slash, colon, asterisk, question mark, quotation mark, less than and greater than signs, vertical bar) cannot be used. Similar rules apply to NetBIOS domain names.

Name registration and resolution steps

The NetBIOS name resolution process usually follows these steps:

1. The client checks the local Hosts file.
2. DNS servers are queried.
3. NetBIOS name resolution is used as a backup.

The NetBIOS node type of the client affects the resolution process. There are four node types: B-Node, P-Node, M-Node, and H-Node. Each uses a different resolution strategy.

Role of the WINS server

WINS (Windows Internet Naming Service) is an important method for NetBIOS name resolution. The WINS server registers and manages the NetBIOS names and IP addresses of computers on the network.

When client computers are switched on, they register their NetBIOS names and IP addresses with the WINS server. These records have a TTL (Time To Live) period. When the registration expires or the IP address of the computer changes, the WINS database is updated.

The main task of WINS is to answer name queries. When a client queries the NetBIOS name of another computer, the WINS server returns the corresponding IP address. In this way, clients can communicate with each other.

WINS is the primary name resolution method, especially for pre-Windows 2000 operating systems. Unlike DNS, it uses a flat namespace and does not have a hierarchical structure. This feature makes it ideal for small and medium-sized networks.

The NetBIOS name resolution process forms the basis of network communication. When configured correctly, this system allows computers to find and communicate with each other seamlessly.

Conclusion

NetBIOS is an important API that facilitates communication in local networks. With its basic components such as Name Service, Session Service and Datagram Service, it allows computers to recognise each other and share data. WINS servers and the NetBIOS name resolution process contribute to the effective operation of this system.

Today, although the use of NetBIOS is decreasing, some applications still depend on this system. Despite the proliferation of DNS-based systems, the role of NetBIOS in network communication cannot be ignored. This technology still maintains its functionality, especially in small and medium-sized networks, and remains an important tool for network administrators.

Frequently Asked Questions About NetBIOS