comparing dns resolvers in the wild n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Comparing DNS Resolvers in the Wild PowerPoint Presentation
Download Presentation
Comparing DNS Resolvers in the Wild

Loading in 2 Seconds...

play fullscreen
1 / 17

Comparing DNS Resolvers in the Wild - PowerPoint PPT Presentation


  • 95 Views
  • Uploaded on

Comparing DNS Resolvers in the Wild. DNS. Domain Name System Translates domain names into IP addresses Hierarchical distributed System Nodes are called as name servers What are resolvers?. Comparing DNS Resolvers in the Wild. DNS has evolved a lot over the years

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Comparing DNS Resolvers in the Wild' - ziazan


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide2
DNS
  • Domain Name System
  • Translates domain names into IP addresses
  • Hierarchical distributed System
  • Nodes are called as name servers
  • What are resolvers?
comparing dns resolvers in the wild1
Comparing DNS Resolvers in the Wild
  • DNS has evolved a lot over the years
  • From a naming service to commodity infrastructure
  • Many third party DNS resolvers have been developed
  • E.g. OpenDNS extends DNS features by adding misspelling correction, phishing protection, and content filtering
  • Do these third party DNS resolvers really improve performance?
content delivery networks
Content Delivery Networks
  • Aim is to provide content with higher availability and performance
  • Brings content closer to the user by using carefully positioned global infrastructure
  • This global infrastructure includes thousands of servers spread world wide
  • Users, when request certain content, are directed to closest CDN server having that data
  • Assumes that DNS resolver is close to the client originating the request
dns today issues
DNS today : Issues
  • CDN’s assumption that DNS resolver is close to the client originating the request may degrade performance
  • A third party DNS which is not in network on the client may direct it to a CDN server out of it’s network
  • CDN’s associate a short TTL on their DNS answers making caching useless
  • “NXDOMAIN catcher” can also hamper some applications like email
dns today issues nxdomain catcher
DNS today : Issues -> NXDOMAIN catcher
  • NXDOMAIN -> Non-Existent Domain
  • NXDOMAIN status code is caught and the IP address of a certain search website is returned
  • Advertisements can be inserted to get profit
measurements

Measurements

We need to compare responsiveness of various DNS resolvers

Local Resolver

OpenDNS

Google

Done by performing DNS queries to 10000 hosts.

Following information collected during the measurements

Vantage Point

Resolver

Host

host selection

Host Selection

DNS relies on caching for efficiency

Selection done by mix of best and worst sites.

Download top 1,000,000 list of sites from Alexa

10,000 hosts selected as follows:

top5000

Most popular hosts which are likely to be in cache

tail2000

Less likely in the cache

embedded

Web-pages containing flash content that browser may have to retrieve from different domain

inside facts of the measurements

Inside facts of the measurements…

Two hosts in same area can query DNS back to back

Response time will be shorter for the second host as the reply will be in cache

Compares response times between first and second query

Need to inspect timestamps in traces to find location

Traces need to be selected that do not interact

evaluation of dns resolvers

Evaluation of DNS resolvers

Generally, local DNS resolvers are used

Third party resolvers claim to provide advanced services that provide web site and phishing site blocking capability along with “suggestions” for failed lookups

Main problem in third party resolvers – larger response time

DNS performance depends of proximity of end hosts

Caching improves the latency with over 95% of second queries answered in less than 100ms

comparison between good isp and bad isp
Comparison between good ISP and bad ISP
  • As can be seen in above diagram, second query has faster response time due to caching
  • For second query in case of bad ISP, local DNS resolver has almost similar delay as others
dns deployment

DNS Deployment

“good ISP”: response times for the second queries show only small variation and are consistently better than those for the first query.

“bad ISP”: scattered along a horizontal and vertical line, as well as the diagonal. We explain this behavior by a load balancing setup without a shared cache.

dns deployment1
DNS Deployment
  • A similar behavior for both OpenDNS and GoogleDNS in several traces.
    • This shows use of load balancing for highly loaded site
  • High RTTs towards the local DNS and load balancing:
    • DNS infrastructure is centralized and requires load balancing to compensate for the high number of queries arriving at a single Location.
  • Load balancing is Good,
    • But the way some ISPs are implementing it prevents caching from being properly utilized.
dns answers
DNS Answers
  • Graph shows that local resolver is more likely to return IP addresses that are in client’s AS than Google or OpenDNS.
  • This locally available content covers akamaized set completely that is local DNS resolvers works better for CDN content.
dns answers1
DNS Answers
  • Graph shows number of different IP addresses returned by Local DNS and Google DNS resolver.
  • As, Local resolver returns IP address in the same AS as client, it can be deduced that Google DNS directs client unnecessarily out of its network.
summary
Summary
  • End-host experiences a very small latency to the resolvers maintained by the local ISP
  • There does exist cases where GoogleDNS and OpenDNS outperform
  • Several ISPs and OpenDNS rely on a load balancing setup without a shared cache, resulting in poor caching efficiency.
  • Third-party DNS resolvers do not manage to redirect the users towards content available within the ISP, contrary to the local DNS ones.