Domain Name System (DNS): Definition & Main components

The Domain Name System (DNS) is a huge network of nameservers that routes DNS queries and makes the Internet possible. There are many things to cover, so let’s jump right into the topic.

Domain Name System (DNS) definition.

The Domain Name System (DNS) is a decentralized, hierarchical network of servers that get questions through DNS queries about domain names (hosts) and answer with DNS records holding the answers. The most common question is where a particular domain name is, and the DNS resolves the question with the IP address where the content is hosted.

Let’s see the main DNS components. 

DNS records

The DNS records are text instructions with various functions like linking domain names to IP addresses, services to hosts, verifying services, and more. They are hosted in a so-called zone file inside DNS servers. The servers can be Primary DNS servers and Secondary DNS servers. The records can be edited only on Primary servers, while the Secondary have only a copy of the records.

DNS query

A DNS query is the question a DNS client asks a DNS server. Depending on the purpose, the client requests different types of DNS records. For example, if a DNS client wants the IP address of Google, he or she will ask for its A or AAAA records that include IP addresses.

Recursive DNS servers

When you perform a DNS query, the Recursive server will be the one that will search for your answer. It is the intermediate that asks other Recursive servers and gets an answer from them or goes to the highest level of authority, the Root servers. It will return the answer to the DNS client and create more queries if the answer is not complete. After the answer is given, it will be saved inside the cache of the Recursive server, the time the TTL of the DNS records indicates.

Authoritative nameservers

The authoritative name servers are those DNS servers that host the original zone file for a domain. They will have the answer for a particular part of the DNS. As we said, it is a hierarchical and decentralized network, so there are many authoritative servers that respond for a particular part of the domain. 

Root servers

The Root servers and Authoritative name servers from the highest level. In a DNS query, they will be the first that will start to answer your query. They will only guide your query to the right Top-Level Domain servers (TLD). There are many main DNS components, but this is the highest.

TLD servers

The TLD servers are authoritative for Top-Level Domains like .com, .de, .it, and so on. They will know where the nameservers of domains, using their TLD, are located. They will answer this part of the query and provide the answer to the Recursive servers.

Authoritative nameservers for domain names and subdomains.

Now, finally knowing the nameservers of a domain name, the Recursive server can ask for the right DNS record or records. The query will be answered, and the result will be returned to the DNS client.

If the DNS query was for a subdomain, then there will be one more level of answer searching. The final answer will come from the authoritative server of the subdomain.