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Content Delivery and Remote DNS services

Explore the use of remote DNS services in Content Delivery Networks (CDNs) to improve web performance by redirecting requests based on client's location. Learn about the effectiveness of EDNS and the potential of passive host proxy and active CDN optimization. Consider alternative solutions like CCN for better optimization.

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Content Delivery and Remote DNS services

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  1. Content Delivery and Remote DNS services jinjian@cnnic.cn, May 11, 2013

  2. Remote DNS • DNS :map names to addresses, or vice versa • A large-scale distributed system • CDNs: leverage DNS for dynamic routing • Current CDN solutions assume proximity between users and their resolvers • Use of remote DNS • Servers concentrated farther from users • Growing third-party DNS services • Public DNS usage has grown to 11% of users! The web performance?

  3. CDN deployment About 74%of the top 1000 web sites use CDNs By Alexa.com

  4. CDNs depend on users DNS to redirect requests CDN: 27% annual increase Remote DNS services break this assumption

  5. Current CDN redirections • CDN redirections • Depends on DNS location, CDN load balancing, network conditions • Overlap zone between locations may be very small.

  6. DNS extension Solution Main idea: directly provide client location to CDN Implemented as an extension: “edns-client-subnet” DNS resolver adds IP prefix of host to request CDN redirection based on location of host. EDNS effectiveness Approximate client location approach typically sufficient

  7. Performance improvement • EDNS solution performance 45% performance improvement Google DNS with ECS

  8. E-DNS • Both DNS and CDN services mustsupport it • only 1% of sites (top 1000) use a non-Google CDN that supports the extension. • Google DNS was the only public service that supports the extension • Why is it not ideal for CDNs to adopt E-DNSsolution?

  9. Clients based solution • Main idea: move the resolver more closer to the user End host directly queries for CDN redirection. So CDN redirection can be based on client’s location • Implementation: Run a DNS proxy on the user’s machine Monitor stream of requests to identify CDN redirections Use Direct Resolution to improve redirection quality Ref to: http://aqualab.cs.northwestern.edu/projects/namehelp

  10. Direct Resolution • Step 1: typical DNS query to recursive resolver Use recursive DNS to translate customer name to CDN • Step 2: directly query CDN for an improved redirection DR map 2 1 Initial map

  11. Problems • Driven by the active host proxy, this solution can not realized dynamic optimization, so it hasn’t played out the advantages of the CDN system. • After the first packet, CDN system knows position information of all hosts ,it is possible to actively change CDN replica for these hosts. • How about “passive host proxy , active CDN optimization”. The passive host proxy only receives commands of CDN system.

  12. Passive host proxy , active CDN optimization • Step 1: typical DNS query to recursive resolver After the first packet, CDN system knows the host’s IP. Initial map

  13. Passive host proxy , active CDN optimization • Step 2: CDN give an improved redirection to the passive proxy Initial map

  14. Passive host proxy , active CDN optimization • Step3: Update redirection Realize dynamic optimization. Initial map

  15. Other solutions? • Better solutions: Don’t change DNS. Don’t change clients. • It is an optimization problem of CDN. The CDN provider should take responsibility for this problem. • A pure CDN based solution ? • CCN? • How?

  16. The End. Thank you !

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