DNS SERVER

Putting it Together

To better illustrate how both of the nameservers interact with each other, let’s imagine that you are at your computer and you want to search for pictures of cats so you type www.google.com into your Web browser to go to Google. However, your computer doesn’t know where the server for www.google.com is located, so your computer sends a query to a recursive DNS nameserver (OpenDNS) to locate the IP address of the website for you. The recursive DNS nameserver is now assigned the task of finding the IP address of the website you are searching for. If the recursive DNS nameserver does not already have the DNS record cached in it’s system, it will then query the authoritative DNS hierarchy to get the answer.

Each part of a domain like www.google.com has a specific DNS nameserver (or group of redundant nameservers) that is authoritative.

At the top of the tree are the root domain nameservers. Every domain has an implied/hidden “.” at the end that designates the DNS root nameservers at the top of the hierarchy. Root domain nameservers know the IP addresses of the authoritative nameservers that handle DNS queries for the Top Level Domains (TLD) like “.com”, “.edu” or “.gov”. It first asks the root domain nameservers for the IP address of the TLD server, in this case, “.com” (for google.com).

Afterwards it asks the authoritative server for “.com”, where it can find the “google.com” domain’s authoritative server. Then “google.com” is asked where to find “www.google.com”. Once the IP address is known for the website the recursive DNS server responds to your computer with the appropriate IP address. The end result of which is that you are now happy because you can search pictures of cats all day long.  Below is an illustration of the process:

Source:https://umbrella.cisco.com/blog/blog/2014/07/16/difference-authoritative-recursive-dns-nameservers/