1. Drafting Behind Akamai (Travelocity-Based Detouring) Dr. Yingwu Zhu

2. Motivation Overlay networks – Build the “view” of the underlying network – Passive and active measurements To determine overlay paths according to some metric, e.g., latency? Redundant, non-scalable, & overhead (expensive!) What common service we may need in place? – An Internet weather-report service

3. Proposed Approach Fact – CDNs (e.g., Akamai) perform extensive network and server measurements Publish the results through DNS over short time scales Can overlay networks recycle 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

4. CDN-Driven One-Hop Source Routing S A1 An A2 …….. D DNS ServerEnE2E1

5. 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

6. 6 DNS “Black Magic” Web Client Akamai High-Level DNS Server Akamai Low-Level DNS Server Local DNS Server PCWorld Authoritative DNS Server PCWorld Web Server Akamai Edge Server Root DNS Server Top-Level Domain DNS Server www.pcworld.com http request/response images.pcworld.com CNAME: a1694.g.akamai.net images.pcworld.com a1694.g.akmai.net 2 ip addresses of Akamai Edge Servers 2 ip addresses of Akamai Edge Servers fetch image files

7. 7 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. PL Node Akamai Edge Server 2 Akamai Edge Server 3 Akamai Low-Level DNS Server.…… Akamai Edge Server 1

8. 8 Initial Results day night BerkeleyPurdue

9. 9 Server Diversity for Yahoo Good overlay-to-CDN mapping candidates Majority of PL nodes see between 10 and 50 Akamai edge-servers Nodes far away from Akamai hot-spots

10. 10 Multiple Akamai Customers Amazon is not hosted on UMass and LBNL Yahoo and NYTimes are not hosted in U. Oregon FEMA is poor!

11. 11 Redirection Dynamics BerkeleyBrazil Korea

12. 12 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

13. 13 Methodology Planet Lab Node Akamai Low-Level DNS Server 10 Best Akamai Edge Servers ………

14. 14 Do CDN redirections correlate to network latencies? (1) Rank = r1+r2-1 – 16 means perfect correlation – 0 means poor correlation Brazil is poorMIT and Amsterdam are excellent

15. 15 Do CDN redirections correlate to network latencies? (2) CNN is poor! 70% paths are among best 10% 97% better than average

16. 16 Akamai-Driven One-Hop Source Routing S A1 An A2 …….. D DNS Server Redirection dynamics sufficiently small for network control EnE2E1 Redirections driven by network conditions Potential for CDN-to-overlay mapping

17. 17 Methodology Source Akamai Low-Level DNS Server Destination Direct Path Akamai path 3 Akamai path 1 ……..... Akamai path 10 Akamai path 2 Akamai path 1 Akamai path 2 Akamai path 3 Akamai path 10

18. 18 Akamai-driven source routing (1) 80% Taiwan 15% Japan 5 % U.S. 75% U.K. 25% U.S. Taiwan-UKUK-Taiwan

19. 19 Akamai-driven source routing (2) Direct paths better than Akamai paths 25% of Akamai paths better than direct paths Akamai and direct paths have similar performance Experiment: US (6), Europe (3), S. America (2), Asia (3)

20. 20 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)

21. 21 Path Pruning Result Direct path accounts for 78% of the gain 2 hours update frequency before the performance declines BTAS better than FAS

22. 22 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