Content Delivery and Remote DNS services jinjian@cnnic.cn, May 11, 2013 Good afternoon, it is Much communication with chinacache Topic:Third-party dns affect cdn and further consideration

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? Originally assume, their locations are very close in network, But recent years, Third-party are grow fast, for sp and end users, Apparently the third party dns can not guarantee So we start to think of under this condition

CDN deployment About 74% of the top 1000 web sites use CDNs This chart shows that the status ,blue, green, and The percentage of real traffic among these websites, pageviews, green bar, is it can be said it is very useful to improve the performance with a cdn solution By Alexa.com

CDNs depend on users DNS to redirect requests CDN: 27% annual increase So generally , First, for a cdn, content origin will synchronize other replica nodes, cdn will have a dynamic routing machanism, Then when an initiate a session using a local dns, directed to server , so if in theory With the growth of remote dns and cdn application, This kind of impact is becoming very phenomenal As a result, it will Cut down the effection of cdn Remote DNS services break this assumption

Current CDN redirections Depends on DNS location, CDN load balancing, network conditions Overlap zone between locations may be very small. According to such analysis, the cdn redirection will be decided by When an end user shift its dns from ,those possible destination of servers may have a little overlap if we do nothing on dns obviously

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 To solve this problem, dns extension solution is raised Main idea convey to cdn system, This way , dns resolver will It is eay to understand, If that, the effectiveness will be very sufficient So google company propose this

Performance improvement EDNS solution performance 45% performance improvement Curve graph shows the performance improvement, With the same condition, if we measure , there will a big improvement com Blue line vs red line Google DNS with ECS

E-DNS Both DNS and CDN services must support 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-DNS solution? This solution require that Currently only 1%. Some large CDNs make their redirection decisions by mapping DNS servers onto a set of\core points"in the network, which are in turn mapped to the CDN's infrastructure [4]; this initial mapping step is Very crucial. Under this approach, the problem is that the CDN cannot directly utilize the information provided by the extension. This issue presents a signicant barrier to adoption of the extension.

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 Naturally, people move their attention to clients, This idea is propose in a public paper, The main idea is to make , that need to run Ref to: http://aqualab.cs.northwestern.edu/projects/namehelp

2 1 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 2 DR map 1 Initial map Step 1 canonical name record Step 2 with this canonical name then get an improved

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.

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

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

Passive host proxy , active CDN optimization Step3: Update redirection Realize dynamic optimization. It is always Optimal Initial map

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?

The End. Thank you ! Thank you all for your time!