DNS (Domain Name System) translates domain names to IP addresses. It is a hierarchical distributed system with name servers at nodes. Third party DNS resolvers like OpenDNS have been developed to add features like phishing protection but may not improve performance over local resolvers. Content delivery networks (CDNs) bring content closer to users via global servers but assume the DNS resolver is near the requesting client, which may not be true for third party resolvers. Measurements show local resolvers generally have lower latency than third parties and are more likely to direct clients to content within their own network, improving performance for CDN content. While third parties can sometimes outperform, many rely on load balancing without caching, resulting in poorer efficiency than

1. DNS
Presented By:
Hogr Goran
Hassan Abbas

2. DNS
• Domain Name System
• Translates domain
names into IP addresses
• Hierarchical distributed
System
• Nodes are called as
name servers
• What are resolvers?

3. 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?

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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.

11. 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.

12. Thank You