The Domain Name System (DNS) is phone book for Internet. All computers on the Internet, from your smart phone or laptop to the servers that serve content for massive retail websites, find and communicate with one another by using numbers. These numbers are known as IP addresses. When you open a web browser and go to a website, you don’t have to remember and enter a long number. Instead, you can enter a domain name like google.com and still end up in the right place.

In other word, The Domain Name System (or DNS) converts human readable domain names (like: http://www.google.com) into Internet Protocol (IP) addresses (like: 173.194.39.78).

How Does It Work

Before we get into how you can use the DNS, we need to understand how the system works. We already know that it maps IP addresses to domain names, but where is this information stored? On nameservers!

Nameservers store DNS records which are the actual file that says “this domain” maps to “this IP address”. So is there a room somewhere that has all the nameservers and DNS records for every site on the Internet? No… that would be ridiculous.

They are actually distributed all around the world. These nameservers are called the root nameservers and instead of storing every domain ever, they store the locations of the TLD (top level domains).

TLD’s are the two or three character like .com that end a domain name. Each TLD has their own set of nameservers that store the information that says who is authoritative for storing the DNS records for that domain.

The authoritative nameservers is typically the DNS provider or the DNS registrar (like Go  Daddy that offers both DNS registration and hosting). And here we can find the DNS record that maps example.com to the IP address 127.66.122.88.

Types of DNS Service

Authoritative DNS: An authoritative DNS service provides an update mechanism that developers use to manage their public DNS names. It then answers DNS queries, translating domain names into IP address so computers can communicate with each other. Authoritative DNS has the final authority over a domain and is responsible for providing answers to recursive DNS servers with the IP address information. Amazon Route 53 is an authoritative DNS system.

Recursive DNS: Clients typically do not make queries directly to authoritative DNS services. Instead, they generally connect to another type of DNS service known a resolver, or a recursive DNS service. A recursive DNS service acts like a hotel concierge: while it doesn’t own any DNS records, it acts as an intermediary who can get the DNS information on your behalf. If a recursive DNS has the DNS reference cached, or stored for a period of time, then it answers the DNS query by providing the source or IP information. If not, it passes the query to one or more authoritative DNS servers to find the information.

What are the steps in a DNS lookup?

For most situations, DNS is concerned with a domain name being translated into the appropriate IP address. To learn how this process works, it helps to follow the path of a DNS lookup as it travels from a web browser, through the DNS lookup process, and back again. Let’s take a look at the steps.

Note: Often DNS lookup information will be cached either locally inside the querying computer or remotely in the DNS infrastructure. There are typically 8 steps in a DNS lookup. When DNS information is cached, steps are skipped from the DNS lookup process which makes it quicker. The example below outlines all 8 steps when nothing is cached.

The steps in a DNS lookup:

1. A user types ‘example.com’ into a web browser and the query travels into the Internet and is received by a DNS recursive resolver.
2. The resolver then queries a DNS root nameserver (.).
3. The root server then responds to the resolver with the address of a Top Level Domain (TLD) DNS server (such as .com or .net), which stores the information for its domains. When searching for example.com, our request is pointed toward the .com TLD.
4. The resolver then makes a request to the .com TLD.
5. The TLD server then responds with the IP address of the domain’s nameserver, example.com. Lastly, the recursive resolver sends a query to the domain’s nameserver.
6. The IP address for example.com is then returned to the resolver from the nameserver.
7. The DNS resolver then responds to the web browser with the IP address of the domain requested initially.
8. Once the 8 steps of the DNS lookup have returned the IP address for example.com, the browser is able to make the request for the web page:
9. The browser makes a HTTP request to the IP address.
10. The server at that IP returns the webpage to be rendered in the browser (step 10).

What is a DNS record?

DNS records (aka zone files) are instructions that live in authoritative DNS servers and provide information about a domain including what IP address is associated with that domain and how to handle requests for that domain. These records consist of a series of text files written in what is known as DNS syntax. DNS syntax is just a string of characters used as commands that tell the DNS server what to do. All DNS records also have a ‘TTL’, which stands for time-to-live, and indicates how often a DNS server will refresh that record.

What are the most common types of DNS record?

• A record – The record that holds the IP address of a domain.
• CNAME record – Forwards one domain or subdomain to another domain, does NOT provide an IP address.
• MX record – Directs mail to an email server.
• TXT record – Lets an admin store text notes in the record.
• NS record – Stores the name server for a DNS entry.
• SOA record – Stores admin information about a domain.
• SRV record – Specifies a port for specific services.
• PTR record – Provides a domain name in reverse-lookups.