When you enter the domain name of your favorite website and watch the page display within seconds, you’re seeing the domain name system (DNS) in action.
The moment you begin a domain search, it’s as though you automatically open the internet’s phonebook (DNS), skim through phone numbers (IP addresses) and their corresponding names (domain names) until you find the one you want and dial. Then you see the website appear.
While this analogy doesn’t exactly explain what goes on behind the scenes, here’s a guide to breakdown what happens within the few seconds from the time you do a domain search until the website shows up on your device’s screen.
Keep reading to learn:
- What domains and domain name servers are
- How domain name servers work
- The process of DNS lookup/resolution
- What DNS caching is
Understanding Domains and Domain Name Servers
Your website (e.g., Bluehost) is your business’s home online, while the domain name (e.g., bluehost.com) is the address with which people visit it.
Essentially, the web is an interconnection of computer networks all around the world. Each computer provides an Internet Protocol (IP) address in the form of numbers to locate individual websites. It usually looks something like 18.104.22.168.
So, instead of cramming these numerical labels (IP addresses) in the address bar before you visit a website, you can use domain names as an easy solution to locate the website of your choice.
This process of locating and identifying websites through IP addresses is the domain name system (DNS).
The domain name system is widely known as the phone book of the internet. When you save phone numbers on your phone, you can locate a particular contact with its equivalent phone number.
Similarly, your computer will only display a website if it understands the numerical equivalent of its domain name.
Specific servers are responsible for providing this information about domain names and their corresponding IP addresses. They are called domain name servers.
These DNS servers are a vital part of the domain name system and how it works. The servers handle queries such as loading a website and its content by translating the domain name into its IP address.
How Domain Name Servers Work
When you type a domain name such as bluehost.com into your browser’s address bar for a domain search, it sends the query to a network of domain name servers managed by its web host for resolution.
The name server information usually looks like ns1.bluehost.com, ns2.bluehost.com. They convert website addresses like example.com to their corresponding IP addresses.
The web host forwards the request to its server, where the website information is stored. It fetches the data and relays it to the browser.
This process of translating domain names to their IP address and displaying the website to a user is called DNS resolution or DNS lookup.
The Process of DNS Lookup/Resolution
DNS lookup is the process of identifying and displaying websites by translating their domain name into numerical codes (their corresponding IP addresses) that computer networks can understand.
The purpose of DNS lookup is to turn a user’s request for a domain search (this is called the DNS query) into the IP address responsible for displaying the requested website.
To understand the process of DNS resolution, let’s take a look at the different domain name servers involved in the process.
The Types of Domain Name Servers
Here are the types of domain name servers and how they interact in the process of DNS resolution during a domain search:
The DNS recursor is also known as the DNS resolver or DNS recursive resolver.
It’s the server assigned to receive search queries from the user’s browser. When a user enters a domain name in the address bar of their website, this DNS query goes to a DNS recursive resolver.
The recursor receives this domain search request and forwards it to the root name server. It initiates the DNS resolution sequence that involves translating that domain name to its corresponding IP address.
Root Name Server
The root name server is the first server that engages the translation process. It receives the DNS query from the DNS recursor for more specific identification in preparation for the top-level domain (TLD) server stage.
The root name server is the server at the root of the domain name system and resolution hierarchy.
TLD Name Server
The top-level domain (TLD) name server receives the DNS query from the recursor, which is the domain search request previously worked upon by the root servers.
The TLD is responsible for keeping all domain names and their extension information. TLD name servers have information for every extension, whether it is a general TLD extension (like .com, .org, or .net), or a location-specific extension (like .uk, .co, or .za).
Authoritative Name Server
After the DNS recursor sends a query to a specific TLD name server, the TLD server sends a signal to the authoritative name server.
It’s the last server in the process of DNS resolution. This authoritative name server has the original records for every IP address and its corresponding website on the internet.
Once it receives the signal from the TLD name server, it searches and returns the IP address for the domain search (the user’s query) back to the DNS Recursor.
The recursor then sends this information to the user’s browser, which displays the requested website.
The Steps Involved in a DNS Lookup/Resolution
Here are the steps involved in DNS resolution, from when a user performs a domain search until the corresponding website displays on their device’s screen.
- A user enters a domain name (like bluehost.com) into their web browser.
- The browser sends the query to a DNS recursive resolver.
- The DNS resolver relays this query to a root server.
- The root server answers the forwarded query with the TLD name server.
- Whether it is a .com, .org, or any other extension, the TLD name server hosts the information about the domain name. The specific TLD server signals an authoritative name server about the DNS query.
- The authoritative name server sends the IP address of the domain (the user’s query) to the DNS recursor.
- The DNS resolver forwards this information to the user’s web browser.
- The web browser makes an HTTP request for that IP address. Then it displays the requested website for the domain name that was entered.
Usually, the DNS information is cached from the initiation of the process either locally or remotely. DNS caching of queries occurs locally in the querying computer or remotely within the DNS sequence.
DNS caching skips steps during the process of DNS lookup. This makes the process of DNS resolution faster. When nothing is cached, a domain search goes through all the steps involved in the DNS lookup process listed above.
DNS caching occurs to temporarily store queries to improve the processing of domain searches and the reliability of the DNS lookup.
The caching of DNS information involves storing DNS data closer to the user who made the query so the domain search is resolved quickly, preventing other processes that may arise during the DNS resolution.
Types of DNS Caching
Here are the types of DNS caching and what they mean:
Browser DNS Caching
Web browsers by default cache DNS information for some time. This is because DNS resolution is quicker when the DNS caching occurs close to the user’s browser that makes a domain search query.
Before a DNS query is processed for resolution, the cache of the user’s browser responsible for sending the query is the first location that’s checked.
Operating System Level DNS Caching
This is the second and last stop for resolution by the stub resolver (also known as DNS client) before the DNS query is handled remotely.
When the stub resolver doesn’t find the record — including the host-to-IP-address translation — for a DNS query in its cache, it sends the query to a DNS recursor on the internet.
The DNS Recursor During DNS Caching
Based on the DNS records available, here’s what the recursor does during DNS caching:
- Even without A records (the most basic DNS records), the DNS recursor will query the authoritative name servers directly if it has NS (name server) records. This skips the querying root and TLD servers steps.
- If the DNS recursor has no NS records, it will skip the root name server querying and move to the TLD servers.
- If the DNS cache is purged (which rarely occurs), the recursor will have no records on the TLD name server and won’t skip any process. Instead, it will query the root name server.
Final Thoughts: How Domain Name Servers Work: The Ultimate Guide
The domain name system is much more than what we see on the front end. This guide describes how the domain name servers work together when a user begins a domain search until the DNS query is resolved.
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