The traditional server-centric design for P2P service discovery is not suitable for ad-hoc environments. In this paper, in order to facilitate the interoperation of ad-hoc environments with other platforms, we introduce D²HT, an algorithm which enables directory federation using DHT, in order to support open scalability. We also introduce the lightweight service discovery (LSD) protocol based on the FIPA compatible agent framework. Our approach overcomes the reconfiguration problems associated with other DHT variants (e.g. Chord [9], CAN [8] and Pastry [10]), which arise when peers join/leave the network, as well as taking into consideration device limitations. We also present an initial implementation of LSD using iPAQs and the D²HT-enabled FIPA Agent Platform.