Julia Evans

The multiple meanings of "nameserver" and "DNS resolver"

I’m working on a zine about DNS right now, so I’ve been thinking about DNS terminology a lot more than a normal person. Here’s something slightly confusing I’ve noticed about DNS terminology!

Two of the most common DNS server terms (“nameserver” and “DNS resolver”) have different meanings depending on the situation.

Now this isn’t a problem if you already understand how DNS works – I can easily figure out what type of “nameserver” is being discussed based on context.

But it can be a problem if you’re trying to learn how DNS works and you don’t realize that those words might refer to different things depending on the context – it’s confusing! So I’m going to explain the different possible meanings and how to figure out which meaning is intended.

the 2 meanings of “nameserver”

There are 2 types of nameservers, and which one the term “nameserver” means depends on the context.

Meaning 1: “authoritative” nameservers

When you update the DNS records for a domain, those records are stored on a server called an authoritative nameserver.

This is what “nameserver” means in the context of a specific domain. Here are a few examples:

  • “Connect a domain you already own to Wix by changing its name servers.”
  • “Almost all domains rely on multiple nameservers to increase reliability: if one nameserver goes down or is unavailable, DNS queries can go to another one.”
  • “You can update the nameserver records yourself by following the steps your domain registrar may provide in the help content at their website”

Meaning 2. “recursive” nameservers, also known as “DNS resolvers”

These servers cache DNS records. Your browser doesn’t make a request to an authoritative nameserver directly. Instead it makes a request to a DNS resolver (aka recursive nameserver) which figures out what the right authoritative nameserver to talk to is, gets the record, and caches the result.

This is what “nameserver” means in the context of you browsing the internet. (“your computer’s nameservers”). Here are a few examples:

  • “Changing nameservers can be a pain on some devices and require multiple clicks through a user interface. On Windows 10, for example…”
  • “Are your DNS nameservers impeding your Internet experience? NEW RELEASE adds nameservers 1.1.1.1, 1.0.0.1 and 9.9.9.9”
  • “Configure your network settings to use the IP addresses 8.8.8.8 and 8.8.4.4 as your DNS servers”

I prefer to use the term “DNS resolver” even though it has 2 meanings because it’s much more commonly used than “recursive nameserver”.

meanings of “DNS resolver”

A DNS resolver can either be a library or a server. (I’m sorry, I know I said that a DNS resolver is a server earlier. But sometimes it’s a library.)

Meaning 1a: “stub resolver” (library version)

A “stub resolver” is something (it can be either a library or a DNS server) which doesn’t know how to resolve DNS names itself, it’s just in charge of forwarding DNS queries to the “real” DNS resolver. Let’s talk about stub resolvers that are libraries first.

For example, the getaddrinfo function from libc doesn’t know how to look up DNS records itself, it just knows to look in /etc/resolv.conf and forward the query to whatever DNS server(s) it finds there.

How you can tell if this is what’s meant: if it’s part of your computer’s operating system and/or if it’s a library, it’s a stub resolver.

Examples of this meaning of “DNS resolver”:

  • “The resolver is a set of routines in the C library that provide access to the Internet Domain Name System (DNS)”
  • “These are the DNS servers used to resolve web addresses. You can list up to three, and the resolver tries each of them, one by one, until it finds one that works.”
  • “If the command succeeds, you will receive the following message “Successfully flushed the DNS Resolver Cache.“”

Meaning 1b: “stub resolver” (server version)

Stub resolvers aren’t always libraries though, like systemd-resolved and dnsmasq are stub resolvers but they’re servers. Your router might be running dnsmasq.

This is also known as a “DNS forwarder”.

How you can tell if this is what’s meant: if your router is running it or it’s part of your OS, it’s probably a stub resolver.

Meaning 2: a recursive nameserver (a server)

A “recursive nameserver” (like we talked about before) is a server that knows how to find the authoritative nameservers for a domain. This is the kind of DNS resolver I was talking about in this A toy DNS resolver post a couple of weeks ago (though mine wasn’t a server).

How to tell if this is what’s meant: if it’s unbound, bind, 8.8.8.8, 1.1.1.1, or run by your ISP, then it’s a recursive nameserver.

Examples of this meaning of “DNS resolver”:

  • “The DNS Resolver in pfSenseĀ® software utilizes unbound, which is a validating, recursive, caching DNS resolver…”
  • “We invite you to try Google Public DNS as your primary or secondary DNS resolver…”
  • “I work for a reasonably large mobile service provider and we are in the process of implementing our own DNS resolver…”

I also did a quick unscientific survey of which terms to refer to DNS servers were the most common by counting Google results. Here’s what I found:

  • dns server: 8,000,000
  • nameserver: 4,200,000
  • dns resolver: 933,000
  • public DNS server: 204,000
  • root nameserver: 42,000
  • recursive resolver: 38,500
  • stub resolver: 26,100
  • authoritative nameserver: 17,000
  • dns resolution service: 9,450
  • TLD nameserver: 7,500
  • dns recursor: 5,300
  • recursive nameserver: 5,060

Basically what this tells me is that by a pretty big margin, the most popular words used when talking about DNS serves are “nameserver”, and “DNS resolver”.

The more specific terms like “recursive nameserver”, “authoritative nameserver”, and “stub resolver” are much less common.

that’s all!

I hope this helps some folks understand what these words mean! The terminology is a bit messier than I’d like, but it seems better to me to explain it than to use less-ambiguous language that isn’t as commonly used in practice.

A toy DNS resolver Things that used to be hard and are now easy