Common Internet File System (CIFS) is a remote file access protocol that forms the basis for Windows file sharing. It is a de facto standard and comes pre-bundled with all Microsoft-based client (e.g. XP) and server (e.g. Server 2003) platforms. Various CIFS implementations (e.g. Samba) are also available for other operating systems such as Linux.

CIFS defines both a client and server: the CIFS client is used to access files on a CIFS server. For example, each time you browse or access files on a Windows server using Windows Explorer, the CIFS protocol is used to transport information (files or directory information) back and forth between your computer and the server you are accessing.

In addition to file sharing, CIFS is also used as a transport protocol for various higher level Microsoft communications protocols, as well as for network printing, resource location services, remote management/administration, network authentication (secure establishment services) and RPC (Remote Procedure Calls).

Each WANJet appliance has a deep understanding of the CIFS protocol and can therefore act on behalf of a CIFS client (e.g. Microsoft XP computer) and server (e.g. Windows Server 2003 computer) to make the interaction between the two much more efficient.