Domain Name System (DNS)
Before the domain name system was implemented, computers used to connect to each other via IP addresses. The domain name system attaches a unique name to this number so that site visitors can easily remember and return to web addresses.
How It Works
When you type a domain name (URL) into the address bar of the web browser, your computer uses DNS to retrieve the current name servers. These name servers point to specific IP address (A records). Finally, your computer sends the request to this IP address along with the web page you are requesting. Every web site has two name servers to which it is pointed.
The process is also called DNS name resolution, which means that the DNS server resolves the domain name to the IP address.
Custom / Private Name Servers
A custom or private name server allows you to run your own name server to respond to DNS requests. It is required for VPS and dedicated hosting, and optional for reseller hosting account.
If you have a reseller account, VPS or Dedicated Server, you can set up private name servers that use your domain name. For example, if you have the domain example.com, you could use ns1.example.com and ns2.example.com for your name servers.
How To Setup Private Name Servers
The first step is to register your private name servers (child name servers) with your domain registrar. For this, you will require corresponding IP addresses, one each for ns1.example.com and ns2.example.com
You can also have same IP address for both the name servers.
In case your website (example.com) is hosted on a different web hosting account (other than reseller, vps, dedicated you are setting name servers for), you also need to add two A records in DNS Management.