How Primary and Secondary DNS Works (with DNS Servers)

In this article how primary and secondary DNS works it will explain the main function of a primary and a secondary DNS server, what the differences are, the most used configurations, and why the service has become a necessity for the domains. 

How Primary and Secondary DNS Works

A Domain Name Server or DNS is perhaps the most underrated piece of technology. And yet, without a DNS Server, it would probably be impossible to simply fire up your favorite browser and go to your website of choice.

In this post, we will see how DNS servers run in the background to make our online surfing experience a pleasant one.

What is DNS?

Often called the phonebook of the Internet, DNS helps point web browsers to the websites they have been commanded to go to. This is done by taking the human friendly universal resource locator (URL), that users enter into a browser’s address bar, and “translating” it into an IP address that is more machine friendly. This IP address points the browser in the right direction and then locates the intended online resource.

What is a DNS server?

A DNS server is a computer with globally spread databases containing the unique public IP addresses associated with the names of every single website, host and other online resources.

DNS servers or domain servers are the hosts where the DNS databases reside. They are interconnected and communicate regularly to synchronize directory information and create redundancy.

There are two types of DNS servers, namely Primary DNS Servers and Secondary DNS Servers.

What is a Primary DNS Server?

A Primary DNS Server is a server that holds the Primary Zone file. This is a master record, that is a read writable file where all resource records for a zone, over which the server has authority, are created, updated, and maintained.

This makes the Primary DNS server the main authoritative DNS server that serves as the initial step for a query when a domain name is translated into an IP address.

What is a Secondary DNS Server?

Secondary DNS Servers exist to serve as standby nameservers. They host the Secondary Zone file. This is a read only copy of the Primary Zone file. The only way it can be updated is by first making changes to the Primary Zone and then synchronizing it with the Secondary Zone files. This is sync process is called a Zone Transfer.

These Secondary DNS Servers allow for an extra set of nameservers that answer queries on behalf of the Primary DNS Servers. If the Primary DNS Server is busy or unreachable, the Secondary DNS Server takes over answering the queries. It is an ideal solution for overcoming redundancy issues caused by misconfigurations, natural disasters, and distributed denial of service (DDoS) attacks attacks, for example.

How Primary and Secondary DNS Works

In the next section of the guide how primary and secondary DNS Works let’s first define the other networking devices that are involved in ensuring we always find the resources we are looking for. They are:

DNS recursive resolver

Also known as a DNS resolver, the DNS recursive resolver is the first to receive queries from DNS clients. It communicates with other DNS servers to find the right IP addresses. Once the resolver has gotten a request it steps in for the client and makes queries to other three DNS servers, namely root nameservers, top level domain (TLD) nameservers and authoritative nameservers.

Root nameservers

The root nameservers are designated for the internet’s DNS root zone – they answer requests about records in the root zone. The replies consist of a list of the authoritative nameservers that go with the correct TLD of a domain name.

Incidentally, and at present, there are only 13 root nameservers designated by alphabets “a” to “m” followed by their domain names.

TLD nameservers

Top Level Domain or TLD nameservers keep the IP addresses of the second level domain (SLD) contained within the TLD name. It then releases the website’s IP address and sends the query to the domain’s nameservers.

Authoritative nameservers

Authoritative nameservers, also known as the domains’ SLD nameservers are the ones that answer DNS queries – they are the ones that are closest to the intended host or resource and return the IP address that is required.

DNS Resolution Architecture Path Example (step by step)

Let’s take an example and see what happens when we want to visit a website. There are 8 steps involved:

    • Let’s say we wanted to go to a website – com, in our case – and we typed the URL into our browser. The browser sends the query to a DNS recursive resolver (step 1).
    • The DNS recursive resolver sends the query to the root DNS nameservers (step 2) to find out which TLD nameservers to head out to. It replies to the recursive resolver (step 3) the address of the TLD DNS server, which has the needed information for the “.com” in the com domain.
    • The recursive resolver sends the information request to the identified TLD nameservers (step 4). And then, the TLD nameserver responds to the recursive resolver (step 5) with the targeted IP address of the domain’s nameservers.
    • The DNS recursive resolver sends the query to the domain’s DNS server (step 6). The domain’s DNS (SLD) server then returns the IP address to the DNS recursive resolver (step 7) for the requested domain.
    • The recursive resolver returns the IP address of the requested domain to our browser (step 8). Lastly, the browser sends an HTTPS request to the IP address, and com returns the targeted webpage or resource, which is then rendered in our browser.

Although each zone must have one Primary DNS Server, it can have any number of Secondary DNS Servers. Maintaining one or more secondary servers ensures that queries can be resolved even if the primary server becomes unresponsive.

Why do we need a secondary DNS Server?

In the example we have just seen, in step 7, where the domain’s DNS servers reply to the recursive resolver so there is a need for a DNS :

  • to reply to the queries at all times. The best way to do that is by adding as many Secondary DNS Servers as may be needed to ensure the service doesn’t fail. It is vital to respond to every sales query so the client has to be shown to the resource or landing page they are looking for.
  •  Administrators need to make sure these potential clients will be able to come and find the site even when the Primary DNS Server is down.
  • Distributes the load between primary and secondary servers.
  • A Secondary DNS Server is not a backup server. There can be more than one Secondary DNS Servers, which means they are there to offset any surges in traffic or a sudden flood of queries that overwhelm the Primary DNS Server.
  • They provide domains with additional active DNS services.
  • When a Secondary DNS Server is included in a configuration, two (or more) authoritative systems respond to queries.
  • Secondary DNS Server helps to Migrate to new DNS infrastructure, with dependencies on old DNS servers.
  • It becomes a standard requirement for Secondary DNS Server. Although domains can have just one DNS server – the Primary DNS server, it makes more financial and business sense to have at least one Secondary DNS Server running alongside it. Right now, it is an accepted Internet standard to ensure domain connectivity at all times.

How Primary and Secondary DNS Works Conclusion

Any website that generates revenue should look Primary and secondary DNS Server. Businesses that can’t afford downtimes need to invest in a secondary DNS server and even perhaps think about another Secondary DNS Server that is located off site for safety reasons.

A secondary DNS can definitely profit your current DNS. It can add extra security, better distribution of the traffic and faster results for your users.

Finally, a secondary DNS server is a cost effective solution that ensures you never experience monetary losses that are a direct result of website inaccessibility  just make sure you hire professionals to configure it correctly.

Avatar for Liku Zelleke
Liku Zelleke

Liku Zelleke is a technology blogger who has over two decades experience in the IT industry. He hasn’t looked back since the day, years ago, when he discovered he could combine that experience with his other passion: writing. Today, he writes on topics related to network configuration, optimization, and security for Cloud Infrastructure Services.

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