Addressing - NetBIOS names

To communicate, each node (computer, printer, router etc) needs to be uniquely identified on a network. Within the TCP/IP suite of protocols, under the IPv4 address scheme, a 32 bit address identifies each node and the network it is connected to. In IPX/SPX networks, a 48 bit address identifies a node on a network and a 32 bit address identifies each network. In NetBIOS networks names are used by each node.

NetBIOS names are 16 bytes (128 bits) long (padded if necessary) and there are very few restraints on the byte values that can be used. Non-alphanumeric characters can be used in NetBIOS names, although some implementations may not support this and applications using NetBIOS may impose other constraints.

Often an implementation will make use of the 16th byte, for example to indicate a particular service; thus the 16th byte may be used in a way which is broadly analogous to port numbers in TCP/IP.

It is worth noting that SMB / CIFS names map directly on to NetBIOS names and in this case the 16th byte is particularly important for identifying various services.

Microsoft has produced a Knowledge Base Article that lists the NetBIOS suffixes (i.e. the sixteenth byte) that Microsoft uses or supports.

The Knowledge Base Article is Q163409 and can be found at;en-us;Q163409

Some examples of the 16th byte in Unique names are given below:

Table 2. Example Unique names

16th byte (in hex) Description
00 Workstation service
01 Messenger service
20 File server service
2B Lotus Notes Server Service

NetBIOS names represent a flat name space; names are non-hierarchical with no provision for subdivision. Because there is no provision for identifying networks with the NetBIOS name scheme, protocols using this name scheme can not be routed.

A NetBIOS name is often associated with one end of a session between two nodes.

A station on the network can be known by several names (aliases) originally up to 12 (See BYTE Magazine November 1989 "Two tin cans and some string" Part 2 Bibliography ) or 17 names (See BYTE Magazine January 1989 "Understanding NetBIOS" Bibliography) . Modern implementations allow very many names to be used. Names can be unique names reserved for the station's exclusive use or group names shared with other stations.

Group Names

Group Names are NetBIOS names that several stations can use. Each Group Name must be unique and in many situations must be distinct from any unique (node) names. These names allow stations to be grouped together to facilitate management and browsing of the network. Stations can send broadcast messages to all stations that share a particular group name.

Within SMB / CIFS environments, collections of systems such as workgroups or domains map on to NetBIOS Group names.

Name Resolution

One name is the permanent node name, which is the physical adapter card's name; this is usually derived from the Media Access Control (MAC) address of the card i.e. the hardware address and consists of 10 bytes of zeros followed by the 6 bytes of the MAC address. This special permanent node name is often called "NETBIOS_NAME_1". It is because one of the names incorporates the physical MAC address (and because there is only one network) that there is often no name resolution protocol (analogous to the Address Resolution Protocol ARP in TCP/IP networks).

When NetBIOS is encapsulated within other protocols such as IPX/SPX or TCP/IP there is a mechanism for mapping NetBIOS names to the address schemes of the encapsulating protocol. See the chapter called Encapsulation in various protocols and encapsulating Encapsulation.