A method for communication in a packet data network including a subnet containing multiple nodes having respective ports. The method includes assigning respective local identifiers to the ports in the subnet, such that each port receives a respective local identifier that is unique within the subnet to serve as an address for traffic within the subnet that is directed to the port. In addition to the local identifiers, respective port identifiers are assigned to the ports, such that at least one of the port identifiers is shared by a plurality of the ports, but not by all the ports, in the subnet. The plurality of the ports are addressed collectively using the at least one of the port identifiers.