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Observations from Router-level Traces

Observations from Router-level Traces. Lisa Amini IBM T. J. Watson Research Center Joint with Henning Schulzrinne, Aurel Lazar Columbia University. Context. Near-term issues facing service providers for Web-facing applications Mirrored servers where to place servers?

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Observations from Router-level Traces

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  1. Observations from Router-level Traces Lisa Amini IBM T. J. Watson Research Center Joint with Henning Schulzrinne, Aurel Lazar Columbia University

  2. Context • Near-term issues facing service providers for Web-facing applications • Mirrored servers • where to place servers? • which network access providers? • how many connection points? • how many servers to deploy? • where to direct clients? • End-to-end routing behavior/delay vs. connectivity • AS level focus

  3. Beyond Connectivity • Inter-domain (AS) routing tables • Aggregation • Policy-based routing • Oregon Route Server Transit Networks B A E D C Autonomous Systems Stub Networks

  4. Traceroute • Router-level end-to-end probing • Traceroute.org website • AS lookup via Routing Arbiter Database (RADB) • Round trip time (RTT) • Loose source-routing • Artifacts

  5. D1 Dataset • 189 sites • Random pairings • Forward and reverse paths • Poisson arrivals • Mean time between probes 10 minutes • 220,551 measurements • 5 days • 1/3 US sites, 2/3 non-US (31 countries) [ Zhang, Duffield, Paxson, Shenker]

  6. Number of Routes Router Hops Router-level Path Length • mean=16.45, std. dev.=4.39

  7. Number of Routes AS Hops AS Path Length • mean=6.47, std. dev.=2.33

  8. AS degree Frequency Rank AS Degree Frequency • Faloutsos3 -0.97 (or higher) correlation coefficient 98% of nodes represented 0.97 correlation coefficient required discarding 31% of nodes

  9. traceroute source Routing view traceroute target Which is correct?

  10. AS frequency Rank AS Frequency 0.97 correlation coefficient required discarding 10% of nodes

  11. Probe Round Trip Time Router Hops AS Hops Response Time Prediction • Does path length predict delay? mean RTT=263ms Correlation coefficient= 0.31 Correlation coefficient =0.27

  12. AS Properties • Can we predict delay based on AS path properties? • Ranked each AS according to: • AS edge degree • AS frequency • Calculated mean RTT per path length • Grouped by top 5, 6-10, 10-20 AS’s

  13. Average RTT Number of Router Hops / Path Influence of Path Properties High edge degree AS?

  14. Average RTT Number of Router Hops / Path High Frequency AS?

  15. Average RTT Number of Router Hops / Path High Edge Degree AS? High edge degree AS in 2 AS hops?

  16. Average RTT Number of Router Hops / Path [http://ratings.metrix.net 7/2001] Backbone AS?

  17. Average RTT Number of Router Hops / Path Backbone AS in 2 AS hops?

  18. Average RTT Number of Router Hops / Path AS Affinity?

  19. Route Asymmetry • Paxson, 1995 • Path(A,B)  Path(B,A) • Issues • Ping triangulation • Congestion Avoidance • Internet mapping A B

  20. AS Hop Differences 11755 paired, unique routes 57% routes were AS-path asymmetric Compare with 30% based on 1995 data 74% asymmetric from first AS hop Number of Routes Number of AS hop differences

  21. Traceroute Issues • AS assignment • [Chang, Jamin, Willinger] AS5 AS6 AS7 AS1 AS2 AS3 AS4

  22. BGP AS Path • Can we predict forward and reverse end-to-end metrics from BGP AS_PATH? • Looking Glass Probing • 92 Sites • 8372 unique path measurements • 2202 fully paired (BGP forward and reverse, traceroute forward and reverse)

  23. Number of Routes Number of AS hop differences AS Hop Differences 47% of forward paths correctly predicted by reverse traceroute 49% of forward paths correctly predicted by reverse BGP AS_PATH 69% of forward paths correctly predicted by forward BGP AS_PATH 34% asymmetry between forward/reverse BGP AS_PATH

  24. Summary • BGP routing tables provide complete view from single location. • Aggregation • Filtering • End-to-end probing from points throughout network can provide insights beyond connectivity • Limited view of connectivity • Traceroute issues with noise, node assignment • BGP AS_PATH inaccurate as path predictor

  25. Discard Criteria • Origin traceroute server not responding • Incomplete traceroute output • Internal use only node address (e.g., 10.x.x.x, 172.16.x.x-172.32.x.x ranges) • Route did note terminate in target AS • Intermediate node did not respond to ICMP echo • No matching reverse probe for same time period

  26. What can we conclude? • Results are for RTT only • Negative results for • Path Length • AS degree, AS frequency, Backbone, hops from origin • High delay as result of transient conditions (congestion)

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