DNS In A nutshell
DNS (the Domain Name System) is one of the most important protocols of the Internet’s infrastructure. DNS allows people to connect to a website like “opendns.com”, without you having to know the website's IP address (after all who wants to remember every websites' IP address). One of our engineers Phillip did an excellent job explaining general DNS mechanics in an earlier OpenDNS blog post, “Speed, Security, and Safety Through DNS”, so I won’t go into much detail here. This article is particularly about the relationship between authoritative and recursive DNS servers.
What Is A Recursive DNS Server?
You might have been able to guess what a recursive DNS server does by is name. It “recurses”, recursive DNS servers are responsible for providing the proper IP address of the intended domain to the requesting host. For example, when making a request to a website from your browser, the host (computer) will then make a request to recursive DNS server to find the IP address associated with the website, this is assuming your operating system and web-browser does not already have it cached. From there the recursive server will check to if the IP is cached and still has a valid time-to-live (TTL). If the recursive server does not have the IP cached it begins the recursive process (repeating a process and referring back to itself) of going through the authoritative DNS server hierarchy, which I will explain further down in this post.
What Are Authoritative DNS Servers?
Simply, authoritative DNS servers are responsible for the IP “mapping” of the intended website. The authoritative servers response to the recursive servers contains important information for each website, such as; corresponding IP addresses, and other necessary DNS records. Authoritative servers are typically managed by web-hosting companies. OpenDNS does NOT provide authoritative DNS services. This matters for both hosting as well as DDNS systems that map domains to dynamic IP addresses.
Putting It Together
Each part of a URL like “www.opendns.com” has a specific DNS server (or group of servers) that is authoritative. Right at the top of the tree are the root domain servers. They know the IP addresses of the authoritative servers that handle DNS queries for the Top Level Domains (TLD) like “.com”. Assuming a particular recursive DNS server doesn’t have any information cached, first it asks the root domain servers what the IP address is of the authoritative servers for the “.com” TLD. Then it asks the authoritative server for “.com” where it can find the “opendns.com” domain’s authoritative server, and so on. Below is an illustration of the process:
Why Does This Matter?
This article was written to generally point out the differences between the two servers. However, authoritative DNS outages happen frequently and can be a big problem. But since you are using OpenDNS, in such a case, you have nothing to worry about. OpenDNS uses SmartCache, which fixes the inaccessibility problem and allows people to visit those sites despite the authoritative server outage.