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SMB

Server message block (SMB) is a popular PC protocol that allows sharing of files, disks, directories, printers, and in some cases, COM ports across a network. SMB is a client/server, request-response-based protocol. Though there are some exceptions to this, most of the communication takes place using the request reply paradigm. Servers make file systems and resources available to clients on the network. Clients can send commands (smbs) to the server that allow them to access these shared resources. SMB can run over multiple protocols, including TCP/IP, NetBEUI, and IPX/SPX. In almost all cases, the NetBIOS interface is used. Microsoft is trying to rename SMB-based networking to Windows Networking and the protocol to CIFS. The SMB protocol is undocumented, although there is a public CIFS group. For more information, refer to the following link on CIFS: ftp://ftp.microsoft.com/developr/drg/CIFS/.

The SMB name service uses well-known UDP and TCP port 137, without requiring a special ALG. For NetBIOS data tunneled through UDP port 138 or TCP port 139, you must configure the NetBIOS ALG. Support for stateful firewall and NAT services requires that you configure the NetBIOS ALG on UDP port 138 and TCP port 139. For SMB name services, both TCP and UDP port 137 must be opened, without a special ALG.

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