Using Samba, Second Edition

An Introduction to the SMB Protocol

Now we’re going to cover some low-level technical details and explore the elementals of the SMB protocol. You probably don’t need to know much about this to implement a simple Samba network, and therefore you might want to skip or skim over this section and go on to the next one (“Windows Workgroups and Domains”) on your first reading. However, assuming you are going to be responsible for long-term maintenance of a Samba network, it will help if you understand how it actually works. You will more easily be able to diagnose and correct any odd problems that pop up.

At a high level, the SMB protocol suite is relatively simple. It includes commands for all the file and print operations that you might perform on a local disk or printer, such as:

• Opening and closing files

• Creating and deleting files and directories

• Reading and writing files

• Searching for files

• Queueing and dequeueing files in a print spool

Each operation can be encoded into an SMB message and transmitted to and from a server. The original name “SMB” comes from the way in which the commands are formatted: they are versions of the standard DOS system-call data structures, or Server Message Blocks, redesigned for transmitting to another computer across a network.

SMB Format

Richard Sharpe of the Samba team defines SMB as a request-response protocol.^[4] 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. In only one rare ...