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Drafting Behind Akamai (TravelocityBased 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/ Drafting Behind Akamai Drafting Detour 2 A. Kuzmanovic Drafting Behind Akamai 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 3 A. Kuzmanovic Drafting Behind Akamai 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 4 A. Kuzmanovic Drafting Behind Akamai 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 5 A. Kuzmanovic Drafting Behind Akamai CDN-Driven One-Hop Source Routing D A1 E1 A2 E2 An En S DNS Server 6 A. Kuzmanovic Drafting Behind Akamai 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 7 A. Kuzmanovic Drafting Behind Akamai DNS “Black Magic” Root DNS Server Akamai High-Level DNS Server Top-Level Domain DNS Server www.pcworld.com www.pcworld.com a1694.g.akmai.net CNAME: images.pcworld.com www.pcworld.com a1694.g.akamai.net Akamai Low-Level PCWorld Authoritative DNS Server a1694.g.akmai.net DNS Server 2 ip addresses of Local DNS Server Akamai Edge Servers images.pcworld.com PCWorld Web Server 2 ip addresses of www.pcworld.com Akamai Edge Servers Akamai Edge Server Web Client 8 A. Kuzmanovic Drafting Behind Akamai 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. Akamai Edge Server 1 Akamai Low-Level DNS Server .…… Akamai Edge Server 3 PL Node A. Kuzmanovic Akamai Edge Server 2 Drafting Behind Akamai 9 Initial Results Berkeley Purdue day night 10 A. Kuzmanovic Drafting Behind Akamai Server Diversity for Yahoo Majority of PL nodes see between 10 and 50 Akamai edge-servers Nodes far away from Akamai hot-spots Good overlay-to-CDN mapping candidates A. Kuzmanovic 11 Drafting Behind Akamai Multiple Akamai Customers Yahoo and NYTimes are not hosted in U. Oregon Amazon is not hosted on UMass and LBNL FEMA is poor! 12 A. Kuzmanovic Drafting Behind Akamai Redirection Dynamics Brazil Berkeley Korea 13 A. Kuzmanovic Drafting Behind Akamai 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 14 A. Kuzmanovic Drafting Behind Akamai Methodology 10 Best Akamai Edge Servers ……… Akamai Low-Level DNS Server Planet Lab Node 15 A. Kuzmanovic Drafting Behind Akamai Do CDN redirections correlate to network latencies? (1) Rank = r1+r2-1 – 16 means perfect correlation – 0 means poor correlation MIT and Amsterdam are excellent Brazil is poor 16 A. Kuzmanovic Drafting Behind Akamai Do CDN redirections correlate to network latencies? (2) 70% paths are among best 10% 97% better than average CNN is poor! 17 A. Kuzmanovic Drafting Behind Akamai Akamai-Driven One-Hop Source Routing Redirections driven by network conditions D Potential for CDN-to-overlay mapping A1 E1 A2 E2 An S DNS Server Redirection dynamics sufficiently small for network control En 18 A. Kuzmanovic Drafting Behind Akamai Methodology Akamai path 1 Akamai path 2 Destination Akamai path 3 Akamai path 1 Akamai path 10 Akamai path 2 Akamai path 3 Akamai Low-Level DNS Server Direct Path Akamai path 10 Source 19 A. Kuzmanovic Drafting Behind Akamai Akamai-driven source routing (1) Taiwan-UK UK-Taiwan 80% Taiwan 15% Japan 5 % U.S. 75% U.K. 25% U.S. 20 A. Kuzmanovic Drafting Behind Akamai Akamai-driven source routing (2) Experiment: US (6), Europe (3), S. America (2), Asia (3) Direct paths better than Akamai paths Akamai and direct paths have similar performance 25% of Akamai paths better than direct paths 21 A. Kuzmanovic Drafting Behind Akamai 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) 22 A. Kuzmanovic Drafting Behind Akamai Path Pruning Result BTAS better than FAS Direct path accounts for 78% of the gain 2 hours update frequency before the performance declines 23 A. Kuzmanovic Drafting Behind Akamai 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 24 A. Kuzmanovic Drafting Behind Akamai