Server Message Block protocol
Get to know the Server Message Block protocol?
The Server Message Block protocol (SMB protocol) is a client-server communication protocol used for sharing access to files, printers, serial ports and other resources on a network. It can also carry transaction protocols for interprocess communication. Over the years, SMB has been used primarily to connect Windows computers, although most other systems — such as Linux and macOS — also include client components for connecting to SMB resources.
A group at IBM developed the SMB protocol in the 1980s. The protocol has since spawned multiple variants, also known as dialects, to meet evolving network requirements over the years. Throughout that time, SMB has been widely implemented and continues to be one of the most popular solutions for file sharing in the workplace.
How does the SMB protocol work?
The SMB protocol enables applications and their users to access files on remote servers, as well as connect to other resources, including printers, mailslots and named pipes. SMB provides client applications with a secure and controlled method for opening, reading, moving, creating and updating files on remote servers. The protocol can also communicate with server programs configured to receive SMB client requests.
Known as a response-request protocol, the SMB protocol is one of the most common methods used for network communications. In this model, the client sends an SMB request to the server to initiate the connection. When the server receives the request, it replies by sending an SMB response back to the client, establishing the communication channel necessary for a two-way conversation.
The SMB protocol operates at the application layer but relies on lower network levels for transport. At one time, SMB ran on top of Network Basic Input/Output System over Transmission Control Protocol/Internet Protocol (NetBIOS over TCP/IP, or NBT) or, to a lesser degree, legacy protocols such as Internetwork Packet Exchange or NetBIOS Extended User Interface. When SMB was using NBT, it relied on ports 137, 138 and 139 for transport. Now, SMB runs directly over TCP/IP and uses port 445.
Today, communications with devices that do not support SMB directly over TCP/IP require the use of NetBIOS over a transport protocol such as TCP/IP.
