Using Samba

An Introduction to SMB/CIFS

We’ll wrap up this chapter with a short tutorial on SMB/CIFS. SMB/CIFS is the protocol that Windows 95/98 and NT machines use to communicate with the Samba server and each other. At a high level, the SMB protocol suite is relatively simple. It includes commands for all of the file and print operations that you might do on a local disk or printer, such as:

• Opening and closing a file

• Creating and deleting files and directories

• Reading and writing a file

• Searching for files

• Queueing and dequeueing files to a print spool

Each of these operations can be encoded into an SMB message and transmitted to and from a server. The original name SMB comes from their data format: these are versions of the standard DOS system-call data structures, or Server Message Blocks, redesigned for transmitting to another machine across a network.

SMB Format

Richard Sharpe of the Samba team defines SMB as a “request-response” protocol.^[16] In effect, this means that a client sends an SMB request to a server, and the server sends an SMB response back to the client. Rarely does a server send a message that is not in response to a client.

An SMB message is not as complex as you might think. Let’s take a closer look at the internal structure of such a message. It can be broken down into two parts: the header , which is a fixed size, and the command string, whose size can vary dramatically based on the contents of the message.

SMB header format

Table 3.1 shows the format of an SMB header. ...