What is a DNS Server?

A DNS server is what tells your browser the IP address of a website. When you navigate to a website, you do so via its domain name. Unfortunately, your web browser doesn’t know how to get to that website’s server with a domain. It needs an IP address.

A DNS server acts as a “phonebook of the internet”. When you navigate to proxidize.com your browser first asks a DNS server what the IP address for the domain is, to know what IP address it needs to send its requests to.

While we normal people talk about DNS servers as one thing, actually resolving a domain name needs different types of DNS server. To keep things clear and simple, we’ll trace a domain resolution request up the entire chain.

Recursive DNS Server

A recursive DNS server is what you and I generally mean when we talk about DNS servers. A recursive DNS server is what a web browser asks to look up a domain name.

Recursive DNS servers, (also called recursive resolvers), don’t store domain-IP data permanently; they go ask other DNS servers whether they know the IP address of the domain and cache that information. They’re distributors, not wholesalers.

These servers receive queries from clients, whether it’s a web browser, computer, phone, router, or even smartfridge. If a recursive DNS server doesn’t know how to resolve the hostnames you’re asking for, they will start asking DNS servers higher up the chain until they find an answer. Once they get the data they need, they will respond to the querying device. This method spares the DNS servers highest up in the hierarchy — the wholesalers — from being overwhelmed.

Root DNS Servers

If the recursive DNS server doesn’t have the domain in its cache, it will contact the next DNS server in the hierarchy: root DNS servers.

Root DNS servers are essentially signposts. A root DNS server directs the recursive DNS server where to go next in function of the domain’s TLD or top-level domain. TLD is everything after the last period ( . ), i.e. .com, .org, .edu, and so on. The root server points the recursive resolver to the appropriate TLD DNS server.

TLD DNS Server

TLD DNS servers have information about domain names under a specific TLD. For example, education.com, education.edu, and education.co.uk are all different websites. Assuming your recursive resolver didn’t have a cached IP address, each domain was resolved through a different TLD DNS server.

TLD DNS servers don’t resolve domains either, they act as referrers like root servers, but about second-level domains, i.e. the “proxidize” part of “proxidize.com”.

Authoritative DNS Server

An authoritative DNS server is a DNS server that contains the DNS data for a domain. This is the final stop. This is where the recursive resolver finds the data on a domain name after you initially pinged it — if the information isn’t found here it doesn’t exist.

Authoritative DNS servers don’t only have the IP address of a domain, though. They have other information that needs DNS resolution like canonical name mappings (i.e. CNAME or how a site makes its cloud-hosted stuff look like its own domain), mail routing (i.e. where does mail get delivered and who’s allowed to email this domain, etc.), and more.

If the server has access to the data requested, it returns the IP address for the requested hostname back to your recursive DNS server.

Other DNS Server Types Overview

There are other types of DNS server we didn’t get into. These support DNS infrastructure or are specific to certain situations or organizations that set up their own infrastructure. 

Here’s a summary overview of the remaining types of DNS server:

• Forwarding DNS Servers: Also called DNS forwarders, these servers forward requests to other resolvers. For example, a large company might want to centralize outbound DNS requests.
• Caching DNS Servers: Alongside recursive resolvers, these servers cache DNS data without doing the full resolution or hosting data permanently like authoritative servers. These can be deployed by ISPs or large organizations to cut down on lookup times.
• Stub Resolvers: Also known as client-side resolvers, these aren’t servers but exist in operating systems to forward DNS requests from applications to a recursive DNS server.
• DNSSEC-Validating Resolvers: These are a security extension for a recursive DNS server that validate digital signatures on DNS data and reject data that’s been modified or tampered with.

Conclusion 

DNS servers are part of the global internet infrastructure and are the reason why we don’t all have to remember a near-infinite number of IP addresses. DNS servers are the infrastructure that make DNS possible and  are the way devices interact with websites by translating the human-readable domain names into IP addresses.

Key Takeaways:

• Behind the term “DNS server” there is a complex network of servers, each operating within its own scope as part of a wider chain.
• A recursive DNS server starts the hostname lookup, chasing down the answer.
• The root and TLD servers direct the recursive resolver to the correct authoritative DNS server.
• DNS caching and the DNS system of servers ensure no authoritative DNS servers get overwhelmed.

When you type in a URL, this sets off a series of requests that (assuming your resolver doesn’t have the answer cached) pass from the resolver to a rootname server, then a TLD server, and on to an authoritative server that has the answer.

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