Different DNS server types

There are many DNS servers globally, but have you thought about what kind of DNS servers they are? There are authoritative DNS servers and recursive DNS servers. Let’s explore together the different DNS servers’ types in detail. 

What is an authoritative DNS server? 

The authoritative DNS servers have the DNS records for the zone they are responsible for and answer the queries coming from the recursive DNS servers. The authoritative DNS nameservers are usually the last step in the domain name resolution process. They can provide an A or an AAAA record with an IP address for the searched domain. 

They can also provide other DNS records like CNAME, PTR, MX, TXT, SRV, and more. 

There are Primary authoritative DNS servers that are responsible for answering queries, but also they have the original zone file, and you can modify the zone file from them. 

There are Secondary authoritative DNS servers that can answer DNS queries, but they have a read-only copy of the zone file. You can’t edit the zone file in a Secondary DNS server. When you have a configuration with Secondary authoritative DNS servers, you can choose their locations and weight. You can use them to balance the load and provide redundancy. 

You can explore the authoritative name server at each step of the DNS hierarchy. There are not only authoritative DNS servers for the domain, but there are authoritative root servers, TLD servers, and subdomain servers. 

Are the root servers authoritative DNS servers?

Yes, the root servers are the group of the highest level in DNS servers. They are authoritative nameservers for the DNS root zone. They answer with the right TLD server, depending on the domain name that was searched. 

Are the TLD servers authoritative DNS servers?

Yes, the TLD servers are authoritative DNS servers too. There are different groups of TLD servers that are responsible for each TLD, like .com, .au, de, etc. The DNS query first will go from a recursive to the root server and back to the recursive. From there, it will be directed to the right TLD server. It answers to the recursive server with the exact, authoritative DNS server that is needed for a domain name. 

What is a recursive DNS server?

A recursive DNS server is the one that acts as a middle-man between the client and the authoritative DNS server and searches for the answer to the query. The client inputs a domain name, its computer will search for the IP address of the domain name. The query will arrive at a recursive server. There, if the answer is inside the DNS cache of the server, it will provide it, and the domain will be resolved. If not, there will be a series of iterative queries until it can resolve the domain or at least orientate to an authoritative server. 

When a recursive server searches and finds the requested DNS records, it will give them to the clients, but it will also keep them inside their cache for faster DNS resolution in the future. 

Conclusion

There could be many levels starting from the root and going down, but what you need to remember is that an authoritative DNS server is the one that holds the DNS records for its zone and a recursive DNS server is the one that retrieves an answer.

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