LAN Manager

LAN Manager was a Network Operating System (NOS) available from multiple vendors and developed by Microsoft in cooperation with 3Com Corporation. It was designed to succeed 3Com's 3+Share network server software which ran atop a heavily modified version of MS-DOS.

Development History

LAN Manager was based on the OS/2 operating system co-developed by IBM and Microsoft. It originally used the Server Message Block protocol atop either the NetBIOS Frames protocol (NBF) or a specialized version of the Xerox Network Systems (XNS) protocol. These legacy protocols had been inherited from previous products such as MS-NET for MS-DOS, Xenix-NET for MS-Xenix, and the afore-mentioned 3+Share. A version of LAN Manager for Unix-based systems called LAN Manager/X was also available.

In 1990, Microsoft announced LAN Manager 2.0 with a host of improvements, including support for TCP/IP as a transport protocol. The latest version LAN Manager, 2.2, which included an MS-OS/2 1.31 base operating system, remained Microsoft's strategic server system until the release of Windows NT Advanced Server in 1993.

Many vendors shipped licensed versions, including:

• 3Com Corporation 3+Open
• HP LAN Manager/X
• IBM LAN Server
• Tapestry Torus

Security Vulnerability

LAN Manager authentication uses a particularly weak method of hashing a user's password known as the LM hash algorithm. This makes the authentication crackable in a matter of seconds using Rainbow Tables or in few hours using brute force. Its use in Windows NT was replaced by NTLM, which is still vulnerable to Rainbow Tables, but less vulnerable to brute force attacks.

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