At some point in the future, how far out we do not exactly know, wireless access to the Internet will outstrip all other forms of access bringing the freedom of mobility to the way we access the we...

ACM SIGCOMM computer communication review

Of the major factors affecting end-to-end service availability, network component failure is perhaps the least well understood. How often do failures occur, how long do they last, what are their causes, and how do they impact customers? Traditionally, answering questions such as these has required dedicated (and often expensive) instrumentation broadly deployed across a network.We propose an alternative approach: opportunistically mining "low-quality" data sources that are already available in modern network environments. We describe a methodology for recreating a succinct history of failure events in an IP network using a combination of structured data (router configurations and syslogs) and semi-structured data (email logs). Using this technique we analyze over five years of failure events in a large regional network consisting of over 200 routers; to our knowledge, this is the largest study of its kind.

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California fault lines: understanding the causes and impact of network failures

We present Hubble, a system that operates continuously to find Internet reachability problems in which routes exist to a destination but packets are unable to reach the destination. Hubble monitors at a 15 minute granularity the data-path to prefixes that cover 89% of the Internet's edge address space. Key enabling techniques include a hybrid passive/active monitoring approach and the synthesis of multiple information sources that include historical data.

With these techniques, we estimate that Hubble discovers 85% of the reachability problems that would be found with a pervasive probing approach, while issuing only 5.5% as many probes. We also present the results of a three week study conducted with Hubble. We find that the extent of reachability problems, both in number and duration, is much greater than we expected, with problems persisting for hours and even days, and many of the problems do not correlate with BGP updates. In many cases, a multi-homed AS is reachable through one provider, but probes through another terminate; using spoofed packets, we isolated the direction of failure in 84% of cases we analyzed and found all problems to be exclusively on the forward path from the provider to the destination. A snapshot of the problems Hubble is currently monitoring can be found at http://hubble.cs.washington.edu.

/pdf/studying-black-holes-in-the-internet-with-hubble-24kgq4luwf.pdf

Studying black holes in the internet with Hubble

A transform domain-based anomaly detection approach to network-wide traffic

Natural and human factors cause Internet outages---from big events like Hurricane Sandy in 2012 and the Egyptian Internet shutdown in Jan. 2011 to small outages every day that go unpublicized. We describe Trinocular, an outage detection system that uses active probing to understand reliability of edge networks. Trinocular is principled: deriving a simple model of the Internet that captures the information pertinent to outages, and populating that model through long-term data, and learning current network state through ICMP probes. It is parsimonious, using Bayesian inference to determine how many probes are needed. On average, each Trinocular instance sends fewer than 20 probes per hour to each /24 network block under study, increasing Internet "background radiation" by less than 0.7%. Trinocular is also predictable and precise: we provide known precision in outage timing and duration. Probing in rounds of 11 minutes, we detect 100% of outages one round or longer, and estimate outage duration within one-half round. Since we require little traffic, a single machine can track 3.4M /24 IPv4 blocks, all of the Internet currently suitable for analysis. We show that our approach is significantly more accurate than the best current methods, with about one-third fewer false conclusions, and about 30% greater coverage at constant accuracy. We validate our approach using controlled experiments, use Trinocular to analyze two days of Internet outages observed from three sites, and re-analyze three years of existing data to develop trends for the Internet.

/pdf/trinocular-understanding-internet-reliability-through-4z4hyhgwkm.pdf

Trinocular: understanding internet reliability through adaptive probing

To maintain high availability in the face of changing network conditions, network operators must quickly detect, identify, and react to events that cause network disruptions. One way to accomplish this goal is to monitor routing dynamics, by analyzing routing update streams collected from routers. Existing monitoring approaches typically treat streams of routing updates from different routers as independent signals, and report only the "loud" events (i.e., events that involve large volume of routing messages). In this paper, we examine BGP routing data from all routers in the Abilene backbone for six months and correlate them with a catalog of all known disruptions to its nodes and links. We find that many important events are not loud enough to be detected from a single stream. Instead, they become detectable only when multiple BGP update streams are simultaneously examined. This is because routing updates exhibit network-wide dependencies.This paper proposes using network-wide analysis of routing information to diagnose (i.e., detect and identify) network disruptions. To detect network disruptions, we apply a multivariate analysis technique on dynamic routing information, (i.e., update traffic from all the Abilene routers) and find that this technique can detect every reported disruption to nodes and links within the network with a low rate of false alarms. To identify the type of disruption, we jointly analyze both the network-wide static configuration and details in the dynamic routing updates; we find that our method can correctly explain the scenario that caused the disruption. Although much work remains to make network-wide analysis of routing data operationally practical, our results illustrate the importance and potential of such an approach.

/pdf/diagnosing-network-disruptions-with-network-wide-analysis-2o1razex0e.pdf

Diagnosing network disruptions with network-wide analysis

This paper investigates the practical issues in applying network tomography to monitor failures. We outline an approach for selecting paths to monitor, detecting and confirming the existence of a failure, correlating multiple independent observations into a single failure event, and applying existing binary networking tomography algorithms to identify failures. We evaluate the ability of network tomography algorithms to correctly detect and identify failures in a controlled environment on the VINI testbed.

/pdf/practical-issues-with-using-network-tomography-for-fault-3pzbwzpbj0.pdf

Yiyi Huang

Papers

Diagnosing network disruptions with network-wide analysis

Practical issues with using network tomography for fault diagnosis