In today’s blog post, we’ll talk about the difference between authoritative and recursive domain name system (DNS) servers. We’ll explain how these two types of DNS servers form the foundation of the internet and help the world stay connected.
What is the domain name system?
Every computer on the Internet identifies itself with an “Internet Protocol” or “IP” address, which is a series of numbers — just like a phone number. That means you can contact any of those computers by typing in the website name, or you can type the IP address into your browser address bar. Either method will get you to the same destination. All servers that host websites and apps on the internet have IP addresses, too.
Give it a try: the IP address of the Cisco Umbrella website is 22.214.171.124.
The domain name system (DNS) is sometimes referred to as the “phone book” of the Internet. You can connect to our website by typing in the IP address in the address bar of your browser, but it’s much easier to type in umbrella.cisco.com. DNS was invented so that people didn’t need to remember long IP address numbers (like phone numbers) and could look up websites by human-friendly names like umbrella.cisco.com instead.
There are too many sites on the Internet for your personal computer to keep a complete list. DNS servers power a website directory service to make things easier for humans. Like phone books, you won’t find one big book that contains every listing for everyone in the world (how many pages would that require? That’s a question for a different blog post.)
There are two types of DNS servers: authoritative and recursive. Authoritative nameservers are like the phone book company that publishes multiple phone books, one per region. Recursive DNS servers are like someone who uses a phone book to look up the number to contact a person or company. Keep in mind, these companies don’t actually decide what number belongs to which person or company — that’s the responsibility of domain name registrars.
Let’s talk about the two different types in more detail.
What is a recursive DNS server?
When you type a website address into your browser address bar, it might seem like magic happens. In reality, the DNS system makes effortless internet browsing possible. First, your browser connects to a recursive DNS server. There are many thousands of recursive DNS servers in the world. Many people use the recursive DNS servers managed by their Internet Service Provider (ISP) and never change them. If you’re a Cisco Umbrella customer, you’re using our recursive DNS servers instead.
Once your computer connects to its assigned recursive DNS server, it asks the question “what’s the IP address assigned to that website name?” The recursive DNS server doesn’t have a copy of the phone book, but it does know where to find one. So it connects to another type of DNS server to continue the search.
What is an authoritative DNS nameserver?
The second type of DNS server holds a copy of the regional phone book that matches IP addresses with domain names. These are called authoritative DNS servers. Authoritative DNS nameservers are responsible for providing answers to recursive DNS nameservers about where specific websites can be found. These answers contain important information for each domain, like IP addresses.
Like phone books, there are different authoritative DNS servers that cover different regions (a company, the local area, your country, etc.) No matter what region it covers, an authoritative DNS server performs two important tasks. First, it stores lists of domain names and their associated IP addresses. Second, it responds to requests from a recursive DNS server (the person who needs to look up a number) about the correct IP address assigned to a domain name. After getting the answer, the recursive DNS server sends that information back to the computer (and browser) that requested it. The computer connects to the IP address, and the website loads, leading to a happy user who can go on with their day.
Putting it all together
This process happens so quickly that you don’t even notice it happening — unless, of course, something is broken.
Let’s use a real world example. Imagine that you are sitting at your computer and you want to search for pictures of cats wearing bow ties (hey, we don’t judge). So you decide to visit Google to do a web search.
First, you type www.google.com into your web browser. However, your computer doesn’t know the IP address of the server for www.google.com. So your computer starts by sending a query to its assigned recursive DNS nameserver. For this example, we’ll assume you’re one of our customers., So it’s a Cisco Umbrella server. Your computer asks the recursive DNS server to locate the IP address of www.google.com. The Cisco Umbrella recursive DNS nameserver is now assigned the task of finding the IP address of the website. Google is a popular website, so its result will probably be cached. But if the recursive DNS nameserver did not already have a DNS record for www.google.com cached in its system, it will need to ask for help from the authoritative DNS hierarchy to get the answer. This is more likely if you are going to a website that is newer or less popular.
Each part of a domain like www.google.com has a specific authoritative DNS nameserver (or group of redundant authoritative nameservers).
At the top of the server tree are the root domain nameservers. Every website address has an implied “.” at the end, even if we don’t type it in. This “.” designates the DNS root nameservers at the top of the DNS hierarchy. The root domain nameservers will know the IP addresses of the authoritative nameservers that handle DNS queries for the Top Level Domains (TLD) like “.com”, “.edu”, or “.gov”. The Umbrella recursive DNS server first asks the root domain nameserver for the IP address of the .com TLD server, since www.google.com is within the .com TLD.
The root domain nameserver responds with the address of the TLD server. Next, the Umbrella recursive DNS server asks the TLD authoritative server where it can find the authoritative DNS server for www.google.com. The TLD authoritative server responds, and the process continues. The authoritative server for www.google.com is asked where to find www.google.com and the server responds with the answer. Once the Cisco Umbrella recursive DNS server knows the IP address for the website, it responds to your computer with the appropriate IP address. Your browser loads Google, and you can get started with more important business: finding pictures of cats in bow ties.
Without DNS, the internet stops working
The DNS system is so important to the modern world that we often refer to it as the foundation of the internet. If your recursive DNS service breaks for some reason, you won’t be able to connect to websites unless you type in the IP addresses directly — and who keeps an emergency list of IP addresses in their desk? If the recursive DNS service you use is working, but has been slowed down for some reason (like a cyberattack), then your connection to websites will be slowed down, too.
Cisco Umbrella launched its recursive DNS service in 2006 (as OpenDNS) to provide everyone with reliable, safe, smart, and fast Internet connectivity. Umbrella has a highly resilient recursive DNS network. We’ve had 100% uptime with no DNS outages in our history. Our 30-plus worldwide data centers use anycast routing to send requests transparently to the fastest available data center with automatic failover.
By configuring your network to use Umbrella’s recursive DNS service, you’ll get the fastest and most reliable connectivity you can imagine. But Umbrella provides much more than just plain old internet browsing. Learn more about how we make the internet a safer place for cats in bow ties in our post about DNS-layer security.