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

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?
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

3. 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

4. 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

5. 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

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
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

7. 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

8. 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.

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
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:

10. 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

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.
It is always Optimal
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 !
Thank you all for your time!