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Understanding the Network Neighborhood
How Linux Works With Microsoft Networking Protocols
by Christopher R. Hertel

SMB Map emboss

SMB, the Server Message Block Protocol, is the most prevalent filesharing protocol on the planet for a very simple reason -- it ships with every Microsoft Windows system and, like it or not, Windows still owns the desktop. Windows is also very common as a server platform in corporate networks. Not content with those markets, Windows is now finding its way into all sorts of new places, including embedded systems, palmtops, and consumer toys. As Windows moves onto new platforms, SMB does too.

Open source operating systems like Linux have been speaking SMB for quite a while now thanks to SAMBA, the well-known open source SMB Server suite. SAMBA, like Windows server products, is primarily a back-room tool. It runs on systems that are mounted in racks or stuck onto shelves in locked server rooms where only the geeks are brave enough to go. If Linux is going to move out of the datacenter and onto the corporate desktop (not to mention homes, hand-helds, cars, etc.), then Linux developers are going to need a working knowledge of SMB -- the native language of the Microsoft Network Neighborhood.

In this article, we'll look into SMB's history and architecture, as well as how its components work together. You'll also find a list of open source projects that aim to make it easier to add SMB support to Linux applications.

A Little History: NetBIOS

SMB Figure 1
Figure One: NetBios running over TCIP/IP.

SMB was originally intended to run over a proprietary network system co-developed by IBM and a company called Sytec. In a moment of obvious inspiration, this system was dubbed "PC-Network." It had no support for routing and could only handle a maximum of about 80 nodes. It was truly LAN-locked.

PC-Network was a broadband LAN product consisting of network cards, cables, and a small device driver known as NetBIOS (Network Basic Input/Output System). The original PC-Network hardware is long gone, having been replaced by Token Ring and then Ethernet. Unfortunately, lots and lots of software was written for use with the NetBIOS Application Programmer's Interface (API), so, even though the PC Network hardware is no longer in use and the NetBIOS device driver is no longer needed, the NetBIOS API has remained as a living artifact.

Instead of moving away from NetBIOS and letting it die an honorable death, several vendors implemented the NetBIOS API on top of other protocols, including DECnet, IPX/ SPX, SNA, and TCP/IP. NetBIOS over TCP/IP is often called NBT and has become the preferred NetBIOS transport. The workings of NBT are described in two Internet Engineering Task Force (IETF) Request For Comment (RFC) documents, RFC1001 and RFC1002 (known collectively as Internet Standard #19). NBT is pictured in Figure One.