NetBIOS resources are referenced by name. Lower-level address information is not available to NetBIOS applications. An application registers one or more names that it wishes to use. The NetBIOS name space is flat and uses sixteen alphanumeric characters. Only 15 characters are available as the last letter is reserved for service type:

The NetBIOS name types describes the functionality:

U : unique - the name may have only one IP address assigned to it. On a network device multiple occurrences of a single name may appear to be registered. The suffix may be the only unique character in the name.

G : group - a normal group; the single name may exist with many IP addresses. WINS responds to a name query on a group name with the limited broadcast address (). Because routers block the transmission of these addresses, the Internet Group was designed to service communications between subnets.

M : multihomed - the name is unique, but due to multiple network interfaces on the same computer this configuration is necessary to permit the registration. The maximum number of addresses is 25.

M : Internet group - a special configuration of the group name used to manage Windows NT Domain names.

D : domain name - new in Windows NT 4.0.

Taken from NetBIOS Suffixes Q163409. Check the original source for updates. Related articles:

RFC1001 - Protocol Standard for a NetBIOS service on a TCP/UDP transport

Q119493 - NetBIOS over TCP/IP Name Resolution and WINS

Q119495 - List of Names Registered with WINS Service

Q154609 - NETBIOS Node Status Query Returns First Instance of Unique Name

Q129603 - Using Systems Management Server Remote Control over a RAS Server

Rhino9 - NetBIOS Shares in depth.