This command was introduced in the LAN Manager 1.0 dialect. It was rendered obsolescent in the NT LAN Manager dialect. NT LAN Manager also removed the transaction-like behavior that supported multiple request and response messages to complete an IOCTL. The command now supports a single request followed by a single response.

This command delivers a device- or file-specific IOCTL request to a server, and a device- or file-specific IOCTL response to the requester. The target file or device is identified by the FID in the request. The request defines a function that is specific to a particular device type on a particular server type. Therefore, the functions supported are not defined by the protocol, but by the systems on which the CIFS implementations execute. The protocol simply provides a means of delivering the requests and accepting the responses.<49>