In this paper, we present C2, a new overlay network based on CAN and Chord. It is primarily designed for a dynamic environment in which peers join and depart the network frequently. For an n-peers C2 system, each peer maintains only about O(log n) of other peers' information, and achieves routing within O(log n) hops. For each peer's joining or departure, C can, in high probability, update the routing tables with no more than O(log n) messages. What distinguishes C2 from many other peer to peer data sharing systems is its low computation cost and its high routing efficiency in a dynamic network. Even in the case that a considerable number of peers fail simultaneously, i.e., several other peers' routing tables are out of date, the average number of hops for successful routing remains acceptable.