A fundamental problem that confronts peer-to-peer applications is to efficiently locate the node that stores a particular data item. This paper presents Chord, a distributed lookup protocol that addresses this problem. Chord provides support for just one operation: given a key, it maps the key onto a node. Data location can be easily implemented on top of Chord by associating a key with each data item, and storing the key/data item pair at the node to which the key maps. Chord adapts efficiently as nodes join and leave the system, and can answer queries even if the system is continuously changing. Results from theoretical analysis, simulations, and experiments show that Chord is scalable, with communication cost and the state maintained by each node scaling logarithmically with the number of Chord nodes.

Chord: A scalable peer-to-peer lookup service for internet applications

This paper presents the design and evaluation of Pastry, a scalable, distributed object location and routing substrate for wide-area peer-to-peer ap- plications. Pastry performs application-level routing and object location in a po- tentially very large overlay network of nodes connected via the Internet. It can be used to support a variety of peer-to-peer applications, including global data storage, data sharing, group communication and naming. Each node in the Pastry network has a unique identifier (nodeId). When presented with a message and a key, a Pastry node efficiently routes the message to the node with a nodeId that is numerically closest to the key, among all currently live Pastry nodes. Each Pastry node keeps track of its immediate neighbors in the nodeId space, and notifies applications of new node arrivals, node failures and recoveries. Pastry takes into account network locality; it seeks to minimize the distance messages travel, according to a to scalar proximity metric like the number of IP routing hops. Pastry is completely decentralized, scalable, and self-organizing; it automatically adapts to the arrival, departure and failure of nodes. Experimental results obtained with a prototype implementation on an emulated network of up to 100,000 nodes confirm Pastry's scalability and efficiency, its ability to self-organize and adapt to node failures, and its good network locality properties.

/pdf/pastry-scalable-decentralized-object-location-and-routing-1u2equbbbp.pdf

Pastry: Scalable, Decentralized Object Location, and Routing for Large-Scale Peer-to-Peer Systems

Hash tables - which map "keys" onto "values" - are an essential building block in modern software systems. We believe a similar functionality would be equally valuable to large distributed systems. In this paper, we introduce the concept of a Content-Addressable Network (CAN) as a distributed infrastructure that provides hash table-like functionality on Internet-like scales. The CAN is scalable, fault-tolerant and completely self-organizing, and we demonstrate its scalability, robustness and low-latency properties through simulation.

https://www.cs.sjtu.edu.cn/~gchen/course/acn/Reading/CAN.pdf

A scalable content-addressable network

Bigtable is a distributed storage system for managing structured data that is designed to scale to a very large size: petabytes of data across thousands of commodity servers. Many projects at Google store data in Bigtable, including web indexing, Google Earth, and Google Finance. These applications place very different demands on Bigtable, both in terms of data size (from URLs to web pages to satellite imagery) and latency requirements (from backend bulk processing to real-time data serving). Despite these varied demands, Bigtable has successfully provided a flexible, high-performance solution for all of these Google products. In this article, we describe the simple data model provided by Bigtable, which gives clients dynamic control over data layout and format, and we describe the design and implementation of Bigtable.

Bigtable: A Distributed Storage System for Structured Data (Awarded Best Paper!).

Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing and distributing information. However, as recent experience shows, the anonymous, open nature of these networks offers an almost ideal environment for the spread of self-replicating inauthentic files.We describe an algorithm to decrease the number of downloads of inauthentic files in a peer-to-peer file-sharing network that assigns each peer a unique global trust value, based on the peer's history of uploads. We present a distributed and secure method to compute global trust values, based on Power iteration. By having peers use these global trust values to choose the peers from whom they download, the network effectively identifies malicious peers and isolates them from the network.In simulations, this reputation system, called EigenTrust, has been shown to significantly decrease the number of inauthentic files on the network, even under a variety of conditions where malicious peers cooperate in an attempt to deliberately subvert the system.

/pdf/the-eigentrust-algorithm-for-reputation-management-in-p2p-hmpmn26kxv.pdf

The Eigentrust algorithm for reputation management in P2P networks

In order to maximize throughput in end-system multicast, it is necessary to have fine-grained control over the transmit load of each participating member. This both avoids bottlenecks where members are overloaded, and allows heterogeneous members to contribute as much transmit capacity as they are able or willing to. In this paper, we describe and simulate an unstructured end-system multicast protocol called Chunkyspread that provides members with fine-grained control over their transmit load, scales well, has relatively low latencies, and can tolerate high membership churn. Chunkyspread is designed as a flexible framework that easily incorporates different constraints and optimizations. For instance, it is straightforward to add titfor-tat or path disjointness as constraints to the system. This paper demonstrates the performance of Chunkyspread through extensive simulations, and provides partial validation of these simulations on Emulab. It also provides detailed comparisons with Splitstream, a structured heterogeneous end-system multicast protocol. The simulations show that Chunkyspread provides far better control over transmit load than Splitstream, while exhibiting comparable or better latency and responsiveness to

/pdf/chunkyspread-heterogeneous-unstructured-end-system-multicast-1jxy9xml2c.pdf

Chunkyspread: Heterogeneous Unstructured End System Multicast

Despite its growing use in critical infrastructure services, the performance of IP(v4) Anycast and its interaction with IP routing practices is not well understood. In this paper, we present the results of a detailed measurement study of IP Anycast. Our study uses a two-pronged approach. First, using a variant of known latency estimation techniques, we measure the performance of current commercially operational IP Anycast deployments from a large number (>20,000) of vantage points. Second, we deploy our own small-scale anycast service that allows us to perform controlled tests under different deployment and failure scenarios. To the best of our knowledge, our study represents the first large-scale evaluation of existing anycast services and the first evaluation of the behavior of IP Anycast under failure.We find that: (1) IP Anycast, if deployed in an ad-hoc manner, does not offer good latency-based proximity, (2) IP Anycast, if deployed in an ad-hoc manner, does not provide fast failover to clients, (3) IP Anycast typically offers good affinity to all clients with the exception of those that explicitly load balance traffic across multiple providers, (4) IP Anycast, by itself, is not effective in balancing client load across multiple sites. We thus propose and evaluate practical means by which anycast deployments can achieve good proximity, fast failover and control over the distribution of client load. Overall, our results suggest that an IP Anycast service, if deployed carefully, can offer good proximity, load balance, and failover behavior.

/pdf/a-measurement-based-deployment-proposal-for-ip-anycast-2mb4iz6otf.pdf

A measurement-based deployment proposal for IP anycast

This paper considers DoS attacks on DNS wherein attackers flood the nameservers of a zone to disrupt resolution of resource records belonging to the zone and consequently, any of its sub-zones. We propose a minor change in the caching behavior of DNS resolvers that can significantly alleviate the impact of such attacks. In our proposal, DNS resolvers do not completely evict cached resource records whose TTL has expired; rather, such resource records are stored in a separate "stale cache". If, during the resolution of a query, a resolver does not receive any response from the nameservers that are responsible for authoritatively answering the query, it can use the information stored in the stale cache to answer the query. In effect, the stale cache is the part of the global DNS database that has been accessed by the resolver and represents an insurance policy that the resolver uses only when the relevant DNS servers are unavailable. We analyze a 65-day DNS trace to quantify the benefits of a stale cache under different attack scenarios. Further, while the proposed change to DNS resolvers also changes DNS semantics, we argue that it does not adversely impact any of the fundamental DNS characteristics such as the autonomy of zone operators and hence, is a very simple and practical candidate for mitigating the impact of DoS attacks on DNS.

/pdf/mitigating-dns-dos-attacks-2729yn5in1.pdf

Mitigating DNS DoS attacks

Due to a limited address space and poor scaling of backbone routing information, the Internet Protocol (IP) is rapidly reaching the end of its useful lifetime. The Simple Internet Protocol Plus (SIPP), a proposed next generation Internet Protocol, solves these problems with larger internet layer addresses. In addition, SIPP provides a number of advanced routing and addressing capabilities including mobility, extended (variable-length) addressing, provider selection, and certain forms of multicast. These capabilities are all achieved through a single mechanism, a generalization of the IP loose source route. We argue that, for reasons of simplicity and evolvability, a single powerful mechanism to achieve a wide range of routing and addressing functions is preferable to having multiple specific mechanisms, one for each function.

/pdf/flexible-routing-and-addressing-for-a-next-generation-ip-4ks18urzgt.pdf

Flexible routing and addressing for a next generation IP

Random peer selection is used by numerous P2P applications; examples include application-level multicast, unstructured file sharing, and network location mapping. In most of these applications, support for a heterogeneous capacity distribution among nodes is desirable: in other words, nodes with higher capacity should be selected proportionally more often.

Random peer selection can be performed over both structured and unstructured graphs. This paper compares these two basic approaches using a candidate example from each approach. For unstructured heterogeneous random peer selection, we use Swaplinks, from our previous work. For the structured approach, we use the Bamboo DHT adapted to heterogeneous selection using our extensions to the item-balancing technique by Karger and Ruhl. Testing the two approaches over graphs of 1000 nodes and a range of network churn levels and heterogeneity distributions, we show that Swaplinks is the superior random selection approach: (i) Swaplinks enables more accurate random selection than does the structured approach in the presence of churn, and (ii) The structured approach is sensitive to a number of hard-to-set tuning knobs that affect performance, whereas Swaplinks is essentially free of such knobs.

/pdf/a-comparison-of-structured-and-unstructured-p2p-approaches-1xjp7l0vbe.pdf

Paul Francis

Papers

Chunkyspread: Heterogeneous Unstructured End System Multicast

A measurement-based deployment proposal for IP anycast

Mitigating DNS DoS attacks

Flexible routing and addressing for a next generation IP

A comparison of structured and unstructured P2P approaches to heterogeneous random peer selection