The convergence of the Grid and Peer-to-Peer (P2P) worlds has led to many solutions that try to efficiently solve the problem of resource discovery on Grids. Some of these solutions are extensions of P2P DHT-based networks. We believe that these systems are not flexible enough in case the indexed data are very dynamic, i.e., the values of the resource attributes change very frequently over time. This is a common case for some data managed by typical Grid systems, like CPU loads, queue occupation, etc. Moreover, since common requests for Grid resources may be expressed as multi-attribute range queries, we think that the DHTbased P2P solutions that have been proposed so far with the aim of supporting such type of queries can suffer from poor flexibility and efficiency.In this paper we thus present a couple of P2P systems. Both the systems are based on Routing Indexes, used to efficiently route queries and update messages in the presence of highly variable data. The first system needs the adoption of a tree-shaped overlay network. The second one, which is an evolution of the first, is based on a two-level hierarchical network topology, where tree topologies must only be maintained at the lower level of the hierarchy, i.e., within the various node groups making up the network. The main goal of the second organization is to achieve a simpler maintenance of the overall P2P graph topology, by preserving the good properties of the tree-shaped topology.We discuss the results of extensive simulation tests aimed at assessing the performance and scalability of the proposed approaches, by also studying how the network topologies affect the propagation of query and update messages.