1 / 26

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?

jovita
Télécharger la présentation

Observations from Router-level Traces

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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)

More Related