NetBIOS Message Block (NMB)

NMB (NetBIOS Message Block) refers to a protocol used in older versions of Windows networking, primarily associated with the SMB (Server Message Block) protocol, which enables file sharing, network browsing, and printer services. NMB is essentially the part of the SMB protocol that handles network name registration, resolution, and browsing.

In NMB, machines on a network are identified by unique NetBIOS names, which are 15 characters long with a 16th character used as a suffix to denote the service type. NMB provides a way for computers on a local network to find each other by name. This can be done via broadcasting (asking all devices on the network), or through a NetBIOS Name Server (NBNS), which is similar to a DNS server but for NetBIOS names.

NMB allows for the browsing of network shares and services. It helps in identifying what services are offered by which machines on a local network. While NMB is part of the broader SMB protocol, it specifically deals with the aspects of networking that involve NetBIOS names. SMB uses NMB for these purposes but also includes other functionalities for file and printer sharing, and later versions have evolved beyond NetBIOS.

In modern networking, the role of NMB (and NetBIOS in general) has diminished. Newer versions of Windows and other operating systems have moved towards using DNS and other mechanisms for network name resolution and service discovery. However, NMB and NetBIOS are still in use in some environments, particularly where older systems are in operation, or for backward compatibility.

NMB and NetBIOS are known to have security vulnerabilities and are often targeted in network attacks. They can reveal information about network structure and machines, and have been used in attacks like SMB Relay. Modern network configurations often involve disabling NetBIOS and NMB to enhance security.