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Inefficiencies of Internet Routing

Inefficiencies of Internet Routing. John Snell Detour Network Research Group (DNRG). AS 2914 Verio. Router. AS 73 UW. Router. Router. Router. Router. Router. Router. Router. Router. Router. AS 3561 MCI. Router. Router. Router. Router. Router. Router. Router. Router.

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Inefficiencies of Internet Routing

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  1. Inefficiencies of Internet Routing John Snell Detour Network Research Group (DNRG) Rosario Retreat

  2. AS 2914 Verio Router AS 73 UW Router Router Router Router Router Router Router Router Router AS 3561 MCI Router Router Router Router Router Router Router Router Router Routing in the Internet • Internet comprised of disorganized independent domains • “Autonomous Systems” (AS) Rosario Retreat

  3. Potential Routing Inefficiencies • Current shortest path metric: AS Hops • Correlates poorly with actual number of hops, latency, bandwidth, drop rate, etc. • Some AS’s have 100’s of routers; some have 2 • Administrative Policy • Refusal to peer • Early Exit • Can’t deliver? Send the packets to nearest AS • Hand-tuned load-balancing • “I think we’ll send more bits through MCI today…” • Thesis: Routing inefficiencies hurt performance Rosario Retreat

  4. Anecdotal Evidence • 1372 > 162 + 142 • Pythagoras lied? • No, the route is flawed • BBN Planet (Walnut Creek) doesn’t peer with Brainstorm.net (Los Altos) • Instead routes via NAP.net in Chicago • Result: Indirect route is ~4.5 times better. (Times in milliseconds) Rosario Retreat

  5. X ax xb A B ab The Experiment • Traceroute to and from numerous points in the network • How often is an indirect path better? • Instead of using edge ab, use ‘edge’ axb • Questions we hope to answer: • How often can I get better round trip latency? • Is poor performance due to congestion? Policy? • What’s the effect of path length? • What about packet loss? Rosario Retreat

  6. Infrastructure & Issues • ~40 freely available traceroute servers (North America) • Just a CGI script on someone’s web server • Free resources, but watch how you use them • If I maintain a load of 40 processes on your web server, are you going to keep that script around? • Measurements sampled randomly, according to a uniform distribution • Each server invoked, on average, every 15 minutes • Only voluntary servers used • Query robots.txt • 21.74% of original set lost due to this nice-nellyism Rosario Retreat

  7. X ax xb A B ab Sources of Measurement Error • Measurements are time averaged • Traceroute servers aren’t routers • The triangle is not regular • Servers don’t represent all possible points • We took all available entry points • Average packet size sent: 40 bytes • Incomplete traces not retained • Trace failure often due to timing out on retrieval • Can’t turn off DNS Resolution Rosario Retreat

  8. Relative Improvement • Half the time we take the non-optimal route Rosario Retreat

  9. Absolute Improvement • Latency gains are non-negligible Rosario Retreat

  10. Diurnal Effects • Static routing policy appears to be at fault, not daytime congestion. Rosario Retreat

  11. Path Length Effect • Lower mean latencies occurring in spite of greater hop counts Rosario Retreat

  12. Packet Loss Effect • Average loss for direct link: ~10%. (0.104213) Rosario Retreat

  13. Absolute Loss • Average loss probability improvement: 0.098006 Rosario Retreat

  14. Relative Loss • Some paths off the scale Rosario Retreat

  15. Read Between the Lines • Gold lines show consistent routing inefficiencies for a given server. • White shows lack of data; #43 is SDSC, an early robots.txt removal Rosario Retreat

  16. Conclusions • On average, ~50% chance of non-optimal routing • Inefficiencies are not small-scale • 14% are 40ms and above, on average • Policy appears to be the primary factor • It doesn’t get better at night • ‘Clustering’ of bad paths • 40% of measured paths could decrease loss probability by a factor of 4 • By Mathis’ result, nearly doubles the TCP bandwidth Rosario Retreat

  17. Future Work • Validation of results by instantaneous path testing • Time averages could be misleading • Inclusion of non-server nodes in the graph • Modem bank entry points {AOL, Compuserve (AOL)} • Popular destinations {Netscape, Yahoo, Disney} • Inclusion of Neal’s 300 new servers • More realistic simulation of Internet behavior • Real-world large-scale network maps • Useful in learning how naming and caching services should be structured Rosario Retreat

  18. Server Locations • Geographically widespread server population Canada Mexico Rosario Retreat

  19. Us R1 R2 Them TTL=1 Time Exceeded! TTL=2 Time Exceeded! TTL=3 Acknowledged. Traceroute • Send a targeted packet with a limited life span, or TTL (Time To Live) • Each hop on the path decrements the TTL by one • If the TTL is zero (post decrement), send back an error message, else forward it • If you’re the recipient, send back an acknowledgement • Each packet sent back contains the sending IP Address • We know who you are • We’re really only using the final acknowledgement Rosario Retreat

  20. Relative Improvement(Mean Latency, > 1.5 times) Rosario Retreat

  21. Relative Improvement (Mean Latency, 1.5 < x < 1.0) Rosario Retreat

  22. Absolute Improvement (Mean Latency, > 50 ms) Rosario Retreat

  23. Absolute Improvement (Mean Latency, 50 ms > x > 0 ms) Rosario Retreat

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