A modular expandable gateway has at least one base module, including a broad-band data communication device for handling communications with an external broad band data communication network, at least one local network port for the connection to a local communication network, a local network interface device adapted to handle communications with the local data communication network and coupled to the local network port through a local network communication bus, the local network interface having a media independent interface and a disable input, a data processing unit interacting with the broad-band data communication device and, through a media independent interface bus connected to the media independent interface, with the local network interface device, so as to enable intercommunication between the local network and the external network; a disable signal line coupled to the disable input of the local network interface device and adapted to drive the local network interface device into a disabled state in which the local network interface device does not engage the media independent interface bus and the local network port, and expansion bus allowing expandability of the gateway by connecting at least one expansion module to the base module, and having the media independent interface bus, the local network communication bus and the disable signal line.