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Understanding the Difference Between a Primary and Secondary DNS Server

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Web Hosting Geek

DNS stands for domain name system, the largest database in the world, containing all registration information pertaining to every domain name in existence. A DNS server, also commonly referred to as a name server, is simply a web server that is equipped with software that allows it to connect and or interact with this database on a regular basis. Data contained within the domain name system includes but is not limited to information related to the web host, the domain registrant, and the active name servers for the domain. Every domain name has at least two name servers, provided by a hosting provider.

Understanding Name Servers

There are literally tens of thousands of DNS servers located throughout the world that each contain a portion of the domain name system database. To maintain redundancy and security of this database there are also 13 root DNS servers that contain the entirety of the database on each server. There are two main types of DNS servers – primary DNS servers and secondary DNS servers. It should be noted that any web server can be used as a DNS server, and any DNS server can be designated as a primary or secondary server. The server administrator has the choice of designating a server as a primary or secondary server, and it is even possible for a single server to be used as a primary server in a zone, while simultaneously being used as a secondary server in another zone.

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What are Primary DNS Servers?

primary dns

A primary DNS server is responsible for reading data related to the domain zone. The primary server is also responsible for communicating with the secondary server. Data pertaining to the domain zone is specifically designated by server administrators, who instruct the server on how to communicate and interact with other web servers. The process of a primary web server communicating with the secondary server is known as a zone transfer, as zone data is being sent from a DNS server to another. Each domain name is assigned to DNS servers for redundancy, and to simplify the process of server administration. If a primary server already contains the zone data for a domain, this data does not need to be replicated because the primary and secondary server continuously share zone data. In basic terms, when a request is issued to a server it travels through the primary DNS server, which then allocates functions to a secondary server.

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What are Secondary DNS Servers?

secondary dns

A secondary DNS server, also commonly referred to as a slave server, is responsible for obtaining zone data from the primary DNS server immediately after being set up. Each time a secondary DNS server functions it receives information from the primary DNS server. However, it should be noted that a secondary DNS server does not necessarily need to obtain information from a primary DNS server, as other secondary servers can be set up as master servers. Secondary servers are nearly as important as primary DNS servers because they offer security through redundancy. Secondary servers also mitigate the total resource load put on the primary DNS server.

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So, What Exactly is DNS?

In the simplest definition, DNS is the term used to describe a system that assigns user-friendly names to unique IP addresses. It translates unfathomable amounts of data into words and phrases in order to provide clear and accurate search results.

See our comprehensive guide to DNS with illustrations, infographics, and PDF.



  • Avatar stephen says:

    Thanks for the nice piece.

    Can you help me understand the following since I did not find that in your article?
    1. Is the replication of data between primary and Secondary DNS servers Async or sync?
    2. Can I deduce that primary data is never always going to be equal to Secondary even if sync replication is used at any point in time?

  • Avatar Manzor Ahmad says:

    Nice data, but need a little bit more explanation.

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