A flooding-based search mechanism is often used in unstructured P2P systems. Although a flooding-based search mechanism is simple and easy to implement, it is vulnerable to overlay distributed denial-of-service (DDoS) attacks. Most previous security techniques protect networks from network-layer DDoS attacks, but cannot be applied to overlay DDoS attacks. Overlay flooding-based DDoS attacks can be more damaging in that a small number of messages are inherently propagated to consume a large amount of bandwidth and computation resources. We propose a distributed and scalable method, DD-POLICE, to detect malicious nodes in order to defend P2P systems from overlay flooding-based DDoS attacks. We show the effectiveness of DD-POLICE by comprehensive simulation studies. We believe that deploying DD-POLICE will make P2P systems more scalable and robust. 1

Keywords: Distributed Hash Tables (DHTs) provide scalable mechanisms for implementing resource discovery services in structured Peer-to-Peer (P2P) networks. However, DHT-based lookups do not support some types of queries that are fundamental in several classes of applications. A way to support arbitrary queries in structured P2P networks is implementing unstructured search techniques on top of DHTbased overlays. This approach has been exploited in the design of DQ-DHT, a P2P search algorithm that combines the Dynamic Querying (DQ) technique used in unstructured networks with an algorithm for efficient broadcast over a DHT. Similarly to DQ, DQ-DHT dynamically adapts the search extent on the basis of the desired number of results and the popularity of the resource to be found. Differently from DQ, DQ-DHT exploits the structural constraints of the DHT to avoid message duplications. The original DQ-DHT algorithm has been implemented using Chord as basic overlay. In this paper we focus on extending DQ-DHT to work in k-ary DHT-based overlays. In a k-ary DHT, broadcast takes only O(log k N) hops using O(log k N) pointers per node. We exploit this “k-ary principle ” in DQ-DHT to improve the search time with respect to the original Chord-based implementation. This paper describes the implementation of DQ-DHT over a k-ary DHT and analyzes its performance in terms of search time and generated number of messages in different configuration scenarios. Peer-to-Peer, resource discovery, dynamic querying, distributed hash tables. ∗ This research work is carried out under the FP6 Network of Excellence CoreGRID funded by the European Commission

Abstract. Dynamic Querying (DQ) is a technique adopted in unstructured Peer-to-Peer (P2P) networks to minimize the number of peers that is necessary to visit to reach the desired number of results. In this paper we introduce the use of the DQ technique in structured P2P networks. In particular, we present a P2P search algorithm, named DQ-DHT (Dynamic Querying over a Distributed Hash Table), to perform DQ-like searches over DHT-based overlays. The aim of DQ-DHT is two-fold: allowing arbitrary queries to be performed in structured P2P networks, and providing dynamic adaptation of the search according to the popularity of the resources to be located. This paper describes the DQ-DHT algorithm using Chord as basic overlay and analyzes its performance in comparison with DQ in unstructured networks. 1

The most prevalent peer-to-peer (P2P) application till today is file sharing, and unstructured P2P networks can support inherent heterogeneity of peers, are highly resilient to peers’ failures, and incur low overhead at peer arrivals and departures. Dynamic querying (DQ) is a new flooding technique which could estimate a proper time-to-live (TTL) value for a query flooding by estimating the popularity of the searched files, and retrieve sufficient results under controlled flooding range for reducing network traffic. Recent researches show that a large amount of peers in the P2P file sharing system are the free-riders, and queries are seldom hit by those peers. The free-riders problem causes a large amount of redundant messages in the DQ-like search algorithm. In this paper, we proposed a new search algorithm, called “AntSearch”, to solve the problem. In AntSearch, each peer maintains its hit rate of previous queries, and records a list of pheromone values of its immediate neighbors. Based on the pheromone values, a query is only flooded to those peers which are not likely to be the free-riders. Our simulation results show that, compared with DQ and its enhanced algorithm DQ+, the AntSearch algorithm averagely reduces 50 % network traffic at almost the same search latency as DQ+, while retrieving sufficient results for a query with a given required number of results. 1.

Abstract—Controlled-flooding algorithms are widely used in unstructured networks. Expanding Ring (ER) achieves low response delay, while its traffic cost is huge; Dynamic querying (DQ) is known for its desirable behavior in traffic control, but it achieves lower search cost at the price of an undesirable latency performance; Enhanced dynamic querying (DQ+) can reduce the search latency too, while it is hard to determine a general optimum parameters set. In this paper, a novel algorithm named Selective Dynamic Query (SDQ) is proposed. Unlike previous works that awkwardly processing floating TTL values, SDQ properly select an integer TTL value and a set of neighbors to narrow the scope of next query. Our experiments demonstrate that SDQ provides finer-grained control than other algorithms: its latency is close to the well-known minimum one via ER; in the mean time its traffic cost also close to the minimum. To our best knowledge, this is the first work capable of achieving best performance in terms of both response latency and traffic cost. In addition, our experiments also demonstrate that SDQ works well in various network topologies. Index Terms—Distributed applications, distributed networks, distributed systems, resource discovery, Selective Dynamic Query, peer-to-peer networks, query algorithm

Abstract—Gradient-based routing using Bloom filters is an effective mechanism to enable data-driven queries in multi-hop networks. A node compressively describes its data items as a Bloom filter, which is then diffused away to the other nodes with information decay. The Bloom filters form an information potential that eventually navigates queries to the source node by ascending the potential field. The existing designs of Bloom filters, however, have critical limitations with respect to the feasibility of gradient-based routing. The compressed routing entries appear to be noisy. Noise in unrelated routing entries is very likely to equal to even outweigh information in right routing entries, thus blinding a query to its desired destination. This work addresses the root cause of the mismatch between the idea and the practical performance of gradient-based routing using Bloom filters. We first investigate the impact of decaying model on the effectiveness of routing entries, and then evaluate the negative impact of noise on routing decisions. Based on such analytical results, we derive the necessary and sufficient condition of feasible gradient-based routing using Bloom filters. Accordingly, we propose a receiveroriented design of Bloom filters, called Wader, which satisfies the above condition. The evaluation results demonstrate that Wader guarantees the correctness and efficiency of gradient-based routing with high probability. I.

Abstract—BL˚ATANT is a peer-to-peer overlay management protocol which aims at maintaining an optimized topology to reduce the cost of broadcasting a message to all peers. BL˚ATANT is based on bio-inspired methodologies that employ ant-like mobile agents and pheromone trails. The overlay maintained by this protocol can be classified as self-structured, because the topology is maintained in an adaptive way in order to fulfill certain criteria, namely an upper bounded diameter and a lower bounded girth (length of the smallest cycle). In this paper we consider the-S variant of the algorithm and focus on its robustness and efficiency in various churn situations. Our goal is to provide an in-depth analysis of the behavior of the protocol in a simulated network using the OverSwarm simulation platform. The obtained results are compared with those of two traditional peer-to-peer protocols, namely CHORD and GIA, in order to achieve a better understanding of the benefits and drawbacks of the considered bio-inspired solution. I.