What Is a Secondary DNS Server?


Scott Campbell

What Is a Secondary DNS Server?

A secondary DNS server, also known as a slave DNS server, is an essential component of a domain name system (DNS) infrastructure. It plays a crucial role in the distribution of DNS queries and the resolution of domain names into IP addresses.

Understanding DNS Hierarchy

In order to understand the purpose of a secondary DNS server, it is important to first grasp the concept of DNS hierarchy. The DNS hierarchy consists of multiple levels, with the root domain at the top and subdomains branching out from it.

Each level in the hierarchy has its own authoritative DNS server responsible for maintaining and distributing information about that particular level. When a user tries to access a website by entering its domain name into a web browser, their device sends a DNS query to its configured DNS server.

The primary DNS server, also known as the master DNS server, is responsible for storing and maintaining the authoritative data for a particular domain. However, relying solely on a single primary server can be risky due to potential issues such as network outages or hardware failures.

The Role of Secondary DNS Servers

This is where secondary DNS servers come into play. A secondary DNS server acts as a backup for the primary server, ensuring redundancy and improving overall system reliability. It mirrors and synchronizes data from the primary server so that it can respond to queries when needed.

When updates or changes are made to the zone records on the primary server, these changes are automatically propagated to all secondary servers through zone transfers. This ensures that all servers within an organization’s infrastructure have consistent and up-to-date information about domain names and their corresponding IP addresses.

Advantages of Using Secondary DNS Servers

  • Improved Redundancy: By having multiple DNS servers, the chances of a complete DNS failure are significantly reduced. If the primary server becomes unavailable, the secondary server can step in and continue serving DNS queries.
  • Load Distribution: Secondary DNS servers help distribute the load of incoming queries across multiple servers.

    This helps to prevent any single server from becoming overwhelmed with traffic and ensures efficient handling of DNS resolutions.

  • Reduced Latency: With secondary DNS servers placed strategically in different geographic locations, users can be directed to a server that is closest to their location. This minimizes network latency and improves overall website performance.

Secondary DNS Configuration

To set up a secondary DNS server, you need to configure it to receive zone transfers from the primary server. This is typically done by specifying the IP address of the primary server as part of the configuration settings on the secondary server.

The zone transfer process can be either full or incremental. In a full zone transfer, all zone data is transferred from the primary server to the secondary server. In an incremental zone transfer, only changes made since the last transfer are synchronized, reducing network traffic and improving efficiency.


A secondary DNS server is an essential component of a robust and reliable DNS infrastructure. By providing redundancy, load distribution, and improved performance, it ensures that users can access websites without interruptions or delays.

By incorporating a secondary DNS server into your organization’s infrastructure, you can enhance your overall network resilience and provide a better user experience for your website visitors.

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