Distributed multicast routing in packet-based communication network devices

This invention generally relates to packet-based data communication networks in which data is transmitted by means of packets which include media access control (MAC) addresses and protocol (IP) address data. The invention relates to an improved manner of organising a device which needs to perform both routing and bridging of internet protocol multicast packets. A network router has a distributed processing scheme for multicast packets. The router has a look-up and forwarding engine operative in response to the reception of an internet protocol multicast packet to direct the packet to a multiplicity of transmit ports which may or may not be connected to the source network segment from which the multicast packet was received by the router. Each transmit port is associated with a predetermined default network segment and the engine directs the packet to the ports (e.g. across the router's backplane) with an identification of the source network segment and control flags which enable processing means associated with the ports to determine by comparison of the respective network segment and the source network segment whether the packet is bridged from the respective port or routed, with relevant modification of the packet, from that port. The control flags comprises a first flag which can be set to allow the relevant modification and a second flag which can be set to allow the comparison between the source segment and the predetermined default segment.