Abstract: The present invention concerns a secure communication system comprising a local network, such as for example of Ethernet type. The system comprises a local network and terminals connected to that network and exchanging data packets. Each terminal includes a table storing the addresses of the groups of terminals with which it can communicate. A terminal which transmits a data packet over the network in multicast mode creates a multicast network address the bits of which, for example high-order bytes, have a given value and which comprises address of the group to which data packet is addressed, each terminal comparing address of the addressee group with content of its table once the network address has been transmitted over the network. The invention is in particular applicable to multifunction communication systems where it is necesssary to ensure high-level security in data transmission, for example for certain systems on board aircraft.