Four types of DNS servers
DNS servers generally fall into four main categories: recursive resolvers, root nameservers, top-level domain (TLD) nameservers, and authoritative nameservers. Each of the four DNS server types has a specific role in the DNS resolution process — find out what each is responsible for.
DNS recursive resolver
A DNS recursive resolver (also called a DNS recursor) acts as a middleman between your device and the other three types of specialized DNS nameservers. These nameservers contain all the necessary information about online domains — their names and respective IP addresses — so that your device can find the website you want to access on the internet.
Whenever you type the domain name (for instance, nordvpn.com) in your browser, a recursive DNS server first checks its cache to find out if you’ve ever visited that website. If you did, a recursor will collect the correct IP address from the cache and instantly connect you to the website.
However, if it’s your first time visiting the website, a DNS recursor will need to issue DNS queries to the remaining three DNS nameservers to connect you to the right webpage.
DNS root nameserver
A DNS root server is the first stop a DNS recursor makes in its search for the website’s IP address. The recursor sends a DNS query to the root server, providing the domain name and asking for information about the correct TLD nameserver for that domain in return.
The root nameserver examines the domain’s extension — if it’s a ".com," ".net," ".org," or any other top-level domain — and informs the DNS resolver which TLD nameserver it needs to examine next to get closer to the website’s IP address.
TLD nameserver
TLD nameservers hold information about the domains with the same extensions, such as ".com.," ".org," or any other progression of letters after the dot in the URL. Each TLD nameserver is responsible for websites with a mutual extension. So a ".com" TLD nameserver contains information on all the websites with the ".com" ending. TLD nameservers are divided into two groups – generic TLDs, such as .com, .org, .edu, and country-code TLDs that are specific to a country, such as .uk, .ca, .us.
The DNS recursive resolver approaches the TLD server to get information on which authoritative nameserver the recursor needs to inquire next.
Authoritative nameserver
An authoritative nameserver is the last stop in the DNS recursor’s search for the right IP address. Each newly created domain name needs to be registered with an authoritative server, which means the server has information about all the available domain names and their respective IP addresses gathered from the DNS record.
Once the DNS recursive resolver finally matches the domain name with the appropriate IP address, it saves the match in its cache so it can connect to the same domain quicker in the future.
