In this paper we present Netalyzr, a network measurement and debugging service that evaluates the functionality provided by people's Internet connectivity. The design aims to prove both comprehensive in terms of the properties we measure and easy to employ and understand for users with little technical background. We structure Netalyzr as a signed Java applet (which users access via their Web browser) that communicates with a suite of measurement-specific servers. Traffic between the two then probes for a diverse set of network properties, including outbound port filtering, hidden in-network HTTP caches, DNS manipulations, NAT behavior, path MTU issues, IPv6 support, and access-modem buffer capacity. In addition to reporting results to the user, Netalyzr also forms the foundation for an extensive measurement of edge-network properties. To this end, along with describing Netalyzr 's architecture and system implementation, we present a detailed study of 130,000 measurement sessions that the service has recorded since we made it publicly available in June 2009.

Distributed Hash Tables (DHT) provide a lookup service in peer-to-peer overlay networks. Many valuable applications have been recently built on top of several available DHTs. However, they function poorly when no direct IP connectivity is available to some nodes (e.g., located behind a NAT or firewall) or in the presence of overloaded or malicious nodes. In this paper, we propose a new method for DHT-based routing called cyclic routing. It generalizes existing single-hop look-ahead approach (also known as ldquoKnow thy neighbor's neighborrdquo) and supports multipath routing. The method provides a systematic way for collecting stable and efficient overlay paths. Cyclic routing has the same theoretical dependability and efficiency upper bounds as basic DHT routing but it is more resilient when IP connectivity is limited or when the overlay suffers from overloaded nodes.

The complexity of modern enterprise networks is ever-increasing, and our understanding of these important networks is not keeping pace. Our insight into intra-subnet traffic (staying within a single LAN) is particularly limited, due to the widespread use of Ethernet switches that preclude ready LAN-wide monitoring. We have recently undertaken an approach to obtaining extensive intra-subnet visibility based on tapping sets of Ethernet switch ports simultaneously. However, doing so leads to a number of measurement calibration issues that require careful consideration to address. First, one must correctly account for redundant copies of packets that appear due to switch flooding, which if not accurately identified can greatly skew subsequent analysis results. We show that a simple, natural rule one might use for doing so in fact introduces systematic errors, but an altered version of the rule performs significantly better. We then employ this revised rule to aid with calibration issues concerning the fidelity of packet timestamps and the amount of measurement loss that our collection apparatus incurred. Additionally, we develop techniques to "map" the monitored network in terms of identifying key topological components, such as subnet boundaries, which hosts were directly monitored, and the presence of "hidden" switches and hubs. Finally, we present initial analyses demonstrating that the magnitude and diversity of traffic at the subnet level is in fact striking, highlighting the importance of obtaining and correctly calibrating switch-level enterprise traces.