magellan: a tool for unicast fault isolation cengiz alaettinoglu packet design llc ramesh govindan...
DESCRIPTION
Goals User's perspective What is of interest to user Internet wide routing monitoring not just an AS History of route changes not just a snapshot Fault diagnosis link/router failure/repairTRANSCRIPT
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Magellan: A Tool for Unicast Fault Isolation
Cengiz AlaettinogluPacket Design LLC
Ramesh GovindanInformation Sciences Institute
John MehringerInformation Sciences Institute
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Motivation
Why can't I reach www.cnn.com? Why is the Internet soooo slow today? It was fine yesterday!
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Goals
User's perspective What is of interest to user
Internet wide routing monitoring not just an AS
History of route changes not just a snapshot
Fault diagnosis link/router failure/repair
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Challenges
Scaling Directed search by correlating destinations Shared learning
Automated heuristics for fault isolation Route change Location of link/router failure/repair Oscillations Others?
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Data Collection
Select target's interesting to the user tcpdump/libpcap Weighting / aging (not implemented)
Initial path to targets traceroute
Monitoring paths Carefully constructed ICMP probes
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Snapshot
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Monitoring
Construct a routing graph Nodes: routers Links: (to, from, source, destination, hop, statistics...)
Probe each link Send two ICMP Echo Request packets to destination
For ttl = hop - 1, hop, verify incident routers, to, from
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Scheduling Probes
WRR schedule a probe for each link Limits the rate of probe packets Weights: some links are more important/interesting
Distance to link No of destinations using it History of volatility
Exponentially averaged
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Test Result
Positive Do nothing
Negative Determine new path
Incremental traceroute from the link upstream and downstream
Determine cause Automatic heuristics based
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Active Fault Isolation
Link failure Probe the link using other destinations that uses it Correlate results
Router failure Generalize on link failure
Oscillations History of old routes Back and forth between a set of routes
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Magellan Components
Magellan Nam
Perl Script
Visualization Offline or real-time Great for debugging/tuning
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Snapshot
Link or router failure I want the nam buttons, etc...
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Effectiveness thru Measurement
Picked 500 popular web sites Yahoo, msn, aol, cnn, ... www.web100.com
Monitored routes to these destinations for 7 days
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Measurements
Number of Link Probes: 839694 Probe per second: 1.39 / second
Total Failures: 2078 Router Failures: 334 Link Failures: 951 Unknown cause: 793
Transients Number of Oscillations: 541
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No of Path Changes
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Effect of Path Length
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Dominant Path
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Cumulative Dominant Path
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Future work: Distributed Magellan
Magellan 1
Magellan 2
Weight to probe inversely proportional to ratio of distances
Shared learning
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Related Work
Topology Maps Router/AS level interconnections Mercator, skitter, AT&T Not all links are usable (routing policy/metrics)
Routing Topology Effect of policy/metrics Npd Vern Paxson's work Focus is on measurement
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Conclusions
Unicast fault isolation User's perspective Automated heuristics History of changes
http://www.isi.edu/scan