Drafting Behind Akamai (Travelocity-Based Detouring)

1. Drafting Behind Akamai (Travelocity-Based Detouring) Aleksandar Kuzmanovic Northwestern University Joint work with: A. Su, D. Choffnes, and F. Bustamante To appear in Sigcomm 2006 http://www.cs.northwestern.edu/~akuzma/

2. Drafting Detour Drafting Behind Akamai

3. Motivation • Overlay networks • Can’t change IP, so change the layers above • E.g., end-point multicast • Common problem • Build the “view” of the underlying network • Passive and active measurements

4. Problem • Independent measurements • Redundant • Non-scalable • Can cause problems • E.g., synchronization • Common service needed • Knowledge plane - MIT • A routing underlay for overlays - Princeton • Network Weather Service - Berkeley

5. Our Approach • Fact • CDNs (e.g., Akamai) perform extensive network and server measurements • Publish the results through DNS over short time scales • Can overlay networks reuse measurements collected by production CDNs? • Significantly reduce the amount of measurements (a complementary service) • No new infrastructure need to be deployed • Inherit the robustness of DNS • Easy integration with existing systems

6. …….. En E2 E1 S A1 An A2 D DNS Server CDN-Driven One-Hop Source Routing

7. Key Questions • How does Akamai work? • DNS translation • How many web replicas does a client see? • Impact of different sites (e.g., Yahoo vs. NY Times)? • DNS redirection dynamics? • Network or server latency? • An example application: one-hop source routing • Mapping CDN servers to overlay nodes • Low-overhead protocols for exploiting CDN redirections

8. Akamai Edge Server PCWorld Web Server Akamai Low-Level DNS Server PCWorld Authoritative DNS Server Local DNS Server Top-Level Domain DNS Server Root DNS Server Akamai High-Level DNS Server Web Client DNS “Black Magic” www.pcworld.com www.pcworld.com a1694.g.akmai.net CNAME: a1694.g.akamai.net images.pcworld.com www.pcworld.com a1694.g.akmai.net 2 ip addresses of Akamai Edge Servers 2 ip addresses of Akamai Edge Servers www.pcworld.com images.pcworld.com fetch image files http request/response

9. Akamai Edge Server 2 Akamai Edge Server 3 Akamai Edge Server 1 Akamai Low-Level DNS Server PL Node Measuring Akamai • 2-months long measurement • 140 PlanetLab (PL) nodes • 50 US and Canada, 35 Europe, 18 Asia, 8 South America, the rest randomly scattered • Every 20 sec, each PL node queries an appropriate CNAME for • Yahoo, CNN, Fox News, NY Times, etc. .……

10. day night Initial Results Berkeley Purdue

11. Nodes far away from Akamai hot-spots Good overlay-to-CDN mapping candidates Server Diversity for Yahoo Majority of PL nodes see between 10 and 50 Akamai edge-servers

12. Yahoo and NYTimes are not hosted in U. Oregon Amazon is not hosted on UMass and LBNL FEMA is poor! Multiple Akamai Customers

13. Brazil Berkeley Korea Redirection Dynamics

14. Key Questions • How does Akamai work? • DNS translation • How many web replicas does a client see? • Impact of different sites (e.g., Yahoo vs. NY Times)? • DNS redirection dynamics? • Network or server latency? • Potentials for one-hop source routing? • Mapping CDN servers to overlay nodes • Low-overhead protocols for exploiting CDN redirections

15. Akamai Low-Level DNS Server Planet Lab Node Methodology 10 Best Akamai Edge Servers ………

16. MIT and Amsterdam are excellent Brazil is poor Do CDN redirections correlate to network latencies? (1) • Rank = r1+r2-1 • 16 means perfect correlation • 0 means poor correlation

17. 70% paths are among best 10% 97% better than average CNN is poor! Do CDN redirections correlate to network latencies? (2)

18. …….. En E2 E1 S A1 An A2 D DNS Server Akamai-Driven One-Hop Source Routing Redirections driven by network conditions Potential for CDN-to-overlay mapping Redirection dynamics sufficiently small for network control

19. Akamai path 1 Akamai path 2 Destination Akamai path 3 Akamai path 1 Akamai path 10 ……..... Akamai path 2 Direct Path Akamai path 3 Akamai path 10 Akamai Low-Level DNS Server Source Methodology

20. 80% Taiwan 15% Japan 5 % U.S. 75% U.K. 25% U.S. Akamai-driven source routing (1) Taiwan-UK UK-Taiwan

21. 25% of Akamai paths better than direct paths Akamai and direct paths have similar performance Direct paths better than Akamai paths Akamai-driven source routing (2) Experiment: US (6), Europe (3), S. America (2), Asia (3)

22. Path pruning • Fact • Not always is Akamai-driven path better than the direct one • Practical issues • How frequently to make a decision whether to use the direct or the Akamai path? • Should one use • the first (of the 2 paths) returned by Akamai (FAS) • the better (of the 2 paths) returned by Akamai (BTAS)

23. BTAS better than FAS 2 hours update frequency before the performance declines Direct path accounts for 78% of the gain Path Pruning Result

24. Conclusions • Reuse measurements performed by CDNs • Reverse-engineering Akamai • DNS redirections sufficiently small • Strong correlation to network conditions • All clients see a large number of paths • CDN-driven one-hop source routing • 25% of Akamai paths outperform direct paths • 50% of nodes “discovered” by Akamai outperform direct paths • Low-overhead pruning algorithms • Global Internet “weather-report” service for little to no cost