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Understanding the Windows Protocols: SMB and CIFS
The Simple Message Block (SMB) protocol provides the basis for Windows file and print sharing. SMB provides support for file browsing and two levels of security:
SMB is implemented on top of a transport protocol. Think of this as similar to the way that AppleTalk exists on top of LocalTalk (serial networking) and EtherTalk (ethernet-based networks).
The SMB protocol has gone through several phases in its existence. Early in life, it used NetBEUI as its transport protocol. NetBEUI is independent of TCP/IP and, as such, was only suited for local-area networks. Today, most SMB services run on top of NetBIOS (NetBT/NBT). NetBIOS is the equivalent of NetBEUI, but running on top of TCP/IP. This creates a routable file/print serving system that can be used across the Internet as well as in LAN situations.
Unfortunately, things aren't that clean and simple. The NetBEUI protocol used a simple broadcast protocol to enable browsing of local resources. When SMB moved to NetBIOS (and thus TCP/IP), finding remote resources became a bigger problem. Machines needed a new way to locate each other, besides sending broadcast packets. This was the only way to successfully handle spanning across multiple subnets.
The Windows Internet Naming Service (WINS) protocol was created to provide a central registration point for Windows computers. When coming online, a computer can register itself with a WINS server as well as look up other machines for creating a connection.
The latest version of SMB is known as Common Internet File System (CIFS) and is backed by Microsoft as well as several third-party companies. CIFS is an open version of SMB with Internet-specific modifications. For the sake of remaining reasonably sane, you can assume that CIFS and SMB are synonymous.
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