The DNS (Domain Name System) translates host names and internet domains to IP addresses. It is a standard technology to manage website names and internet domains. A DNS server is a computer which is registered to join DNS. DNS servers interact with each other using Private Network Protocol. There are two basic kinds of DNS: Primary and Secondary DNS. They are DNS server computers where the domain name is saved. The information is identical on both DNS servers. The values for these two DNS's are configured by the Internet Service Provider (ISP). The secondary DNS acts as backup for the Primary DNS in case the Primary DNS does not work.
The DNS service enables you to make use of names like [www.ccm.net/] instead of writing the IP address (such as 18.104.22.168).
The IP address of websites are rather difficult to remember, thus the need to create a system that makes the "resolution" (translation) between IP and name.
To achieve this translation, special servers are used (DNS servers). Every computer connected to the internet is configured with a list of servers which is automatically filled in by your ISP.
The secondary DNS acts as a backup for the primary DNS in case the latter does not work. There is no guarantee that the first DNS work at all times.
The above clearly explains why all domain name should imperatively have 2 DNS server with a fixed IP address.