Abstract: A data transfer system comprises interconnected network devices organized to constitute a hierarchical logical arrangement having at least three levels of network hierarchy. A network device (102) receives from another network device (101) that is higher at the hierarchy a first data item such as an IP-prefix defining a first set of network addresses such as IP-addresses. The network device composes second data items so that each of the second data items defines one of mutually non-overlapping sub-sets of the first set. The network device transmits the second data items to network devices (104, 105) that are lower at the hierarchy in order to allocate one of the sub-sets to each of these network devices at the lower level of the hierarchy. This procedure can be repeated on all levels of the network hierarchy. Thus, the address configuration can propagate downwards through the hierarchical logical arrangement of the network devices.