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My Thoughts on Public DNS and Global Traffic Traffic Management

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My Thoughts on Public DNS and Global Traffic Traffic Management

· Performance Zone ·
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Last weekend I read this good paper on Public DNS and Global Traffic Management, written by scientists over at Microsoft Research. The paper on IEEE Xplore is available only for members, but if you have access, it's worth reading it.

One of the main points of this paper is:

It appears that Google, as an cloud service provider, exactly achieves this goal by offering its own Public DNS service. When clients switching from ISP-assigned LDNS to Google Public DNS, their performance accessing Google services will improve, as Google's GTM can now observe the clients' IP and select data centers that are client-best, rather than DNSbest. However, when the clients access any other cloud services, their performance will inevitably degrade. The best data center determined by the GTMs of those services, can only be DNS-best with respect to Google DNS servers. Because the Google DNS servers are further away from the clients than ISP-assigned LDNS, the performance perceived by the clients will be worse than before switching to the Public DNS system.


When using Public DNS, the conclusion at the time was "when the clients access any other cloud services, their performance will inevitably degrade".

And in my opinion, although Public DNS systems may not match the LDNS performance currently when it comes to best datacenter selection, they can get better by having more DNS servers around the world. Any concern about performance should be gone once these Public DNS companies catch up.

The other point is that other companies that have DNS servers with special load balancing method will have less data, therefore making poorer decisions for customers. In a way, Public DNS takes away some of the power these companies have. But the same argument applies, with more DNS servers by Public DNS providers, they should get back to the current state, with similar amount of information.

For technologists, typically the answer on whether to use Public DNS or ISP's Local DNS boils down to what is faster. Google, in particular, has a very interesting caching layer shared by all DNS servers that help it be even faster. So why now use it, like asked here: Should I use my ISP's DNS, or Google's The answer has been plain simple: measure its performance and switch to it if it's faster.


The concern, though, is that any company providing such service would be able to learn the behavior of customers and monetize this by more targeted ads. Google denies such use in their FAQ section and on their Privacy Page, so in theory they do not relate DNS usage to any personally identifiable information. The question is whether this is honored and how much can be inferred about usage even without any PII in their logs.

Business Goal

No service is offered for free without aligning with the business goals, so when one reads "We built Google Public DNS to make the web faster and to retain as little information about usage as we could" (from Public DNS Privacy Page), there must be at least some business purpose for this Public DNS. The first thought, as mentioned above in the quoted text, is that Google can improve their customer's experiences, but since they control the client-side, they could provide more information about the user through Javascripts embedded in their page code, for instance. So the question is, besides that, what is the purpose behind Public DNS?

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