DNS Lookups - Forwards & Backwards Reader

In this course you will learn about DNS lookups, and how to perform both forward and reverse DNS lookups.  As a bonus we will introduce you to a few free online services that can do even more than traditional DNS lookups.

Introduction to DNS - What it is, and why it matters (copy)

DNS Defined

The Domain Name System (DNS) is a hierarchical decentralized naming system for computers, services, or any resource connected to the Internet or a private network.

Source: https://en.wikipedia.org/wiki/Domain_Name_System


Here's the nickel tour:  Computers communicate over networks using IP addresses, not system names.  So when you try to surf to www.example.com your computer has to first look up that system name using DNS to figure out that computer's IP address, which is then used to make the connection.

An analogy would be looking up someone's name in your Phone Contacts to find their phone number, then you dial the phone number.


Enter the meaning of each letter for DNS

The D in DNS stands for  

The N in DNS stands for  

The S in DNS stands for  

Forward Lookup (copy)

Forward DNS lookup

When doing a DNS lookup (also called a forward lookup) the DNS query takes a host name (e.g. www.example.com) as input and gives that host's IP address as output (e.g.

This assumes the host name exists in a DNS server somewhere.


There are cases where a host name is non-existent, and therefore will not forward lookup into an IP address.

Here is an example of a non-existing system name (assuming somebody does not register it in the near future):

Forward DNS lookup result for a non-existent host name

Below is an example of a successful (forward) DNS lookup for www.example.com:

Successful forward DNS lookup

Define the input and output for a forward DNS lookup

The input (or thing being looked up) by a forward DNS lookup is the  

The output (or thing returned) by a forward DNS lookup (if successful) is the