1. A method for marking traffic in a packet-switched data network, in which the packet-switched data network comprises a distributed hierarchical naming system and customer premises equipment; in which the customer premises equipment comprises a marking rule store for storing marking rules, in which each marking rule is indicative of a quality of service level allocated to a connection impinging on the customer premises equipment; in which the method comprises: deriving from the distributed hierarchical naming system quality of service data for a connection; storing in the marking rule store a marking rule for the connection based on the derived quality of service data; and marking traffic on the connection in accordance with the marking rule; in which the quality of service data for the connection comprises quality of service data corresponding to at least one network of the connection, in which an address of the connection comprises a series of address bits arranged in order of significance from a least significant bit position to a most significant bit position, in which the method comprises: sending a series of queries in succession to the distributed hierarchical naming system to derive quality of service data corresponding to at least one network of the connection; in which each one of the series of successive queries is associated with a masked form of the address of the connection; in which each masked form of the address comprises a series of contiguous address bits that occurs in the address of the connection and a series of contiguous masked bits set to a common value; in which the series of contiguous masked bits comprises the least significant address bit position and the series of contiguous address bits comprises the most significant bit position, in which each subsequent query in the series is associated with a masked form of the address of the connection which comprises more masked bits and a correspondingly lower number of the address bits occurring in the address of the connection when compared with the masked form of the address with which the immediately previous query in the series is associated; in which the method further comprises: terminating the series of queries upon receipt from the distributed hierarchical naming system of an indication indicating that the most recent query of the series relates to a valid address selecting the quality of service data derived in response to the most recent query of the series of queries; based on the selected quality of service data, storing in the marking rule store a marking rule for the network corresponding to the most recent query; and marking traffic on the connection in accordance with the marking rule.