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Recursive DNS: What Is It?

(This post has been updated from its original publish in Aug 2010)

You’ve probably heard the term before: Recurisve DNS. So what is it? And how does it compare to Authoritative DNS services such as Dyn Managed DNS?

Recursive DNSPlain And Simple

Recursive DNS is essentially the opposite of Dyn Managed DNS which is an authoritative DNS service that allows others to find your domain while Recursive DNS allows you to resolve other people’s domains.

Let’s Dive Deeper

Recursive DNS provides recursive DNS. Yes, that’s recursive (something which repeats or refers back to itself) and confusing. In order to make a distinction between the service we provide and the general concept of recursive DNS, here’s an explanation:

To better illustrate how recursive DNS works, let’s imagine you are sitting at a computer in your home. You’re connected to the Internet by a cable connection and you are surfing the web looking for widgets. You have no idea where to find widgets, so you open your web browser and type in http://www.google.com.

This is when recursive DNS kicks in. Your web browser looks to see if it knows where to find the machine “www.google.com.” If it doesn’t have this info stored in its own cache, it will ask your operating system (OS) if it knows where to find this host. If your OS doesn’t have this in its cache, your OS will perform a DNS query to find that info. That query will go to the DNS servers provided by your ISP and these servers are configured to provide recursive DNS.

To simplify things, the ISP’s name server will send a query to the “root” name servers to find out who is responsible for the .COM domain (i.e. which name servers are authoritative for the .COM domain). Once it has this info, it will send a DNS query to those name servers asking them who is responsible for the google.com domain and then a final query to those name servers asking for the address of www.google.com.

Those servers which answer for google.com and resolve www.google.com to an IP address? Those are authoritative DNS servers (like our Dyn Managed DNS service except we don’t provide DNS for Google).

Where Recursive DNS Services Come Into Play

Sometimes, an ISP’s recursive DNS servers get overloaded and the queries you send to them can start timing out. When this happens, you can’t find www.google.com and so you can’t search for widgets.

Why are your ISP’s recursive DNS servers overloaded? It could be any number of reasons, but it happens. In any case, there are Recursive DNS services such as Dyn Internet Guide that provide an alternative set of servers that you can use in place of your ISP-provided name servers. Specialized Recursive DNS services often offer much better performance, reliability, capacity, and in some cases filtering capabilities to control what web sites can be accessed via the service for security or content reasons.


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Whois: Chris Gonyea

Chris Gonyea is Product Manager, Traffic Management at Dyn, a cloud-based Internet Performance company that helps companies monitor, control, and optimize online infrastructure for an exceptional end-user experience. Follow on Twitter (@ChrisGonyea and @Dyn).