Map Network Drive dialog in Windows 10, connecting to a local SMB network drive
Server Message Block (SMB) is a communication protocol used to share files, printers, serial ports, and miscellaneous communications between nodes on a network. On Windows, the SMB implementation consists of two Windows services: "Server" (ID: LanmanServer) and "Workstation" (ID: LanmanWorkstation). It uses NTLM or Kerberos protocols for user authentication. It also provides an authenticated inter-process communication (IPC) mechanism.
SMB was originally developed in 1983 by Barry A. Feigenbaum at IBM to share access to files and printers across a network of systems running IBM PC DOS. In 1987, Microsoft and 3Com implemented SMB in LAN Manager for OS/2, at which time SMB used the NetBIOS service atop the NetBIOS Frames protocol as its underlying transport. Later, Microsoft implemented SMB in Windows NT 3.1 and has been updating it ever since, adapting it to work with newer underlying transports: TCP/IP and NetBT. SMB over QUIC was introduced in Windows Server 2022.
In 1996, Microsoft published a version of SMB 1.0 with minor modifications under the Common Internet File System (CIFS By default, a Microsoft Windows NT 4.0 server used NetBIOS to advertise and locate services. NetBIOS functions by broadcasting services available on a particular host at regular intervals. While this usually makes for an acceptable default in a network with a smaller number of hosts, increased broadcast traffic can cause problems as the number of hosts on the network increases. The implementation of name resolution infrastructure in the form of Windows Internet Naming Service (WINS) or Domain Name System (DNS) resolves this problem. WINS was a proprietary implementation used with Windows NT 4.0 networks, but brought about its own issues and complexities in the design and maintenance of a Microsoft network.
Since the release of Windows 2000, the use of WINS for name resolution has been deprecated by Microsoft, with hierarchical Dynamic DNS now configured as the default name resolution protocol for all Windows operating systems. Resolution of (short) NetBIOS names by DNS requires that a DNS client expand short names, usually by appending a connection-specific DNS suffix to its DNS lookup queries. WINS can still be configured on clients as a secondary name resolution protocol for interoperability with legacy Windows environments and applications. Further, Microsoft DNS servers can forward name resolution requests to legacy WINS servers in order to support name resolution integration with legacy (pre-Windows 2000) environments that do not support DNS.
Network designers have found that latency has a significant impact on the performance of the SMB 1.0 protocol, that it performs more poorly than other protocols like FTP. Monitoring reveals a high degree of "chattiness" and a disregard of network latency between hosts. For example, a VPN connection over the Internet will often introduce network latency. Microsoft has explained that performance issues come about primarily because SMB 1.0 is a block-level rather than a streaming protocol, that was originally designed for small LANs; it has a block size that is limited to 64K, SMB signing creates an additional overhead and the TCP window size is not optimized for WAN links. Solutions to this problem include the updated SMB 2.0 protocol, Offline Files, TCP window scaling and WAN optimization devices from various network vendors that cache and optimize SMB 1.0 and 2.0.
History
editSMB 1.0
editBarry Feigenbaum originally designed SMB at IBM in early 1983 with the aim of turning DOS INT 21h local file access into a networked file system. Microsoft made considerable modifications to the most commonly used version and included SMB support in the LAN Manager operating system it had started developing for OS/2 with 3Com around 1990. Microsoft continued to add features to the protocol in Windows for Workgroups (mfsymlink option. Docker on Windows also seems to use it."Lan Manager Networking Concepts". Support. Microsoft. Archived from the original on December 30, 2012. Retrieved September 18, 2014.
- Leach, Paul J.; Naik, Dilip C. (January 10, 1997). "CIFS/E Browser Protocol". Archived from the original on May 31, 2024. Retrieved December 10, 2017.
- Leach, Paul J.; Naik, Dilip C. (December 19, 1997). "A Common Internet File System (CIFS/1.0) Protocol". Archived from the original on May 31, 2024. Retrieved December 10, 2017.