LANMAN

LANMAN, usually written as LANMAN or LAN Manager, can refer to two related concepts in computer networking.

First, LAN Manager denotes a family of network operating systems developed by Microsoft—in collaboration with 3Com—during the late 1980s and early 1990s. These MS LAN Manager products provided client-server file and print services and used NetBIOS/SMB networking to support Windows-based workstations and servers. The LAN Manager generation helped establish early Windows networking, interoperability with other NetBIOS networks, and laid groundwork that influenced later Microsoft networking technologies, including authentication approaches used in Windows NT.

Second, LAN Manager is also associated with the LAN Manager authentication protocol, commonly called the LM or LM hash. This cryptographic scheme was used by LAN Manager and by early Windows versions for password verification. The LM approach converts passwords to uppercase, splits them into 7-character chunks, and uses DES to produce a hash. It has a 14-character password limit and is known to be insecure because of its predictability and vulnerability to offline attacks. As a result, modern Windows systems discourage or disable LM hashing in favor of more secure methods, such as NTLM and its successors (NTLMv2). The term NT LAN Manager (NTLM) is a later authentication protocol that built on and superseded the older LAN Manager approach in many environments.

In contemporary practice, LAN Manager and its LM hash are largely considered legacy infrastructure. Best practices recommend disabling LM hashing, enforcing strong passwords, and using modern authentication protocols and encryption.