What is DNS? How Does the Domain Name System Work on the Internet?

What is DNS (Domain Name System), and how does entering a domain name allow you to access a website? Behind this seemingly simple action lies a DNS server system that is constantly at work. This article will help you understand DNS in the simplest, most memorable way!

What is DNS?

DNS (Domain Name System) is a system that translates human-friendly domain names like www.vcloudia.com into numerical IP addresses that computers can understand, such as 203.113.xxx.xxx.

To put it simply, DNS acts like the phonebook of the Internet:

- Humans remember domain names

- Computers communicate using IP addresses

- DNS serves as the translator between both sides

Without DNS, users would have to memorize long strings of complex IP numbers every time they access a website.

What is the Domain Name System used for?

The Domain Name System keeps the Internet running smoothly through its core functions:

- Resolving domain names into accurate IP addresses: DNS converts easy-to-remember domain names like www.vnetwork.vn into numerical IP addresses that computers can understand and use. Thanks to this, browsers know exactly which server to connect to in order to load website content.

- Helping browsers identify the correct website hosting server: Every website is hosted on one or more different servers. DNS serves as a locator, guiding the browser to find the correct server managing the domain name, avoiding misdirected access or missing data.

- Accelerating access speed through caching mechanisms (cache - buffer memory): DNS has the capability to temporarily store resolution results for a specific period of time. When users revisit the same website, the system can respond immediately without querying from scratch, reducing latency and improving page load speeds.

- Reducing the burden of memorizing IP addresses for users: Instead of having to memorize complex numeric IP strings, users only need to remember simple, human-readable domain names. DNS handles all the conversion in the background, making the Internet experience friendlier and easier to use.

Thanks to DNS, you only need to enter a website name, while the entire process of locating the server, establishing the connection, and displaying content is handled automatically in the background.

DNS helps users locate the exact server hosting a website, but protecting that server against malicious requests is the responsibility of another layer: WAF (Web Application Firewall). A WAF sits in front of websites and web applications, blocking malicious requests according to OWASP standard rule sets before they ever reach the server. Enterprises can experience this protective layer for free starting today.

What is a DNS Server? DNS Servers involved in loading a web page

A DNS Server (Domain Name System server) is a server that stores domain name resolution information and answers DNS queries from users or web browsers. Each DNS Server plays a distinct role in the query chain, ensuring that finding the correct IP address happens quickly and accurately.

There are 4 primary types of DNS Servers involved in the DNS resolution process:

1. DNS Recursor (DNS resolving server)

The DNS Recursor is the first point of contact that receives the request from the user's browser. It is responsible for making requests on behalf of the client to other DNS Servers until it finds the final answer.

You can think of the DNS Recursor as a librarian tasked with tracking down a specific book in a library.

2. Root Name Server (Root server)

The Root Name Server is the starting point for every DNS query. This server does not store specific IP addresses, but instead points the way to servers that manage top-level domains such as .com, .vn, or .net.

3. TLD Name Server (Top-Level Domain Server)

TLD Servers manage domain name extensions, such as:

- .com

- .net

- .org

For example, with viettelidc.com.vn, the TLD Server would be .vn, and it directs the query further to the authoritative server managing that specific domain name.

4. Authoritative Name Server

This is the ultimate source of truth, where the definitive DNS records of the domain name are stored. Once a query reaches here, the DNS Server returns the precise IP address for the domain name requested by the user.

Thanks to the close coordination among DNS Servers - from the DNS Recursor to the Authoritative Name Server - the domain resolution process is executed rapidly and accurately, enabling users to access websites smoothly without needing to worry about the underlying technical steps.

What is a DNS Resolver and what role does it play?

After understanding the types of DNS Servers involved in domain name resolution, it is essential to clarify a vital intermediary component: the DNS Resolver.

A DNS Resolver is the component positioned between the user and the DNS Server system, responsible for receiving domain resolution requests from browsers or applications, and then determining how to process them to locate the corresponding IP address.

A DNS Resolver can operate in two ways:

- Responding immediately if cached data exists (cache - buffer memory): When the DNS Resolver has previously resolved the domain name and the data remains valid, it returns the result immediately without forwarding queries to upstream DNS Servers. This approach reduces latency and enhances website access speeds.

- Continuing to query DNS Servers if information is unavailable: In cases where data is not present in the cache, the DNS Resolver sequentially dispatches queries to DNS Servers such as Root Name Servers, TLD Name Servers, and Authoritative Name Servers to identify the accurate IP address.

DNS Resolvers typically reside across multiple tiers, including:

- Web browsers, helping rapidly handle repetitive queries

- Operating systems, acting as an intermediary prior to querying out to the Internet

- Internet Service Providers (ISPs), which operate large-scale DNS Resolvers serving extensive user bases

Thanks to the DNS Resolver, the DNS resolution workflow is organized efficiently, curtailing unnecessary queries and ensuring users are consistently connected to the right website in a rapid and reliable manner.

How does the DNS resolution process work?

When you type www.example.com into your browser, the DNS resolution process typically proceeds through the following steps:

- The browser sends a request to the DNS Recursor: The browser or operating system sends a domain name resolution request to the DNS Recursor. This server acts as an intermediary responsible for locating the corresponding IP address for the domain name entered by the user.

- The DNS Recursor queries the Root Name Server: If the DNS Recursor does not already have the information available in its cache, it sends a query to a Root Name Server. The root server does not supply the IP directly; rather, it directs the DNS Recursor on where to search next.

- The Root Server points to the TLD Name Server (.com): The Root Name Server responds with the address of the TLD Name Server corresponding to the domain extension, such as .com, .vn, or .org, to proceed with the lookup.

- The TLD Server points to the Authoritative Name Server: The TLD Name Server identifies and delivers the address of the Authoritative Name Server - the authoritative DNS server directly managing the example.com domain.

- The Authoritative Server returns the IP address: The Authoritative Name Server checks the DNS data for the domain and returns the exact IP address to the DNS Recursor. This represents the final result of the resolution process.

- The browser uses the IP address to load the website: The DNS Recursor sends the IP address back to the browser, whereupon the browser connects to the web server and retrieves the website content to display to the user.

This entire process takes merely a few milliseconds. Thanks to this multi-tiered DNS resolution sequence, browsers consistently locate the correct server in an extremely short timeframe, enabling website access to occur almost instantaneously without users ever noticing the back-end processing steps.

Just as DNS automatically handles the entire server-finding process in the background, a WAF automatically filters and blocks malicious traffic at the web application layer without requiring manual operations from engineering teams.

Common types of DNS queries

During the DNS resolution process, the system employs various query types to strike a balance between accuracy and response speed. The three most common types of DNS queries include:

- Recursive Query: With a recursive query, the client (browser or operating system) demands that the DNS Resolver return the ultimate result - namely the exact IP address of the domain - or an error message if it cannot be found. Users do not need to concern themselves with any of the intermediate steps behind the scenes.

- Iterative Query: In an iterative query, each DNS Server responds with the best information it holds, typically a referral to the next DNS Server in the hierarchy. The DNS Resolver relies on these referrals to follow up with subsequent queries until reaching the final result.

- Non-recursive Query: A non-recursive query takes place when the DNS Server or DNS Resolver already possesses the requested information in its cache or serves as the authoritative server for that domain. In this scenario, the result is returned immediately without executing additional queries.

The flexible combination of recursive, iterative, and non-recursive queries empowers the DNS architecture to simultaneously ensure high precision and optimize response speeds as users navigate the Internet.

What is DNS Cache? Why does DNS accelerate access?

In practice, not every DNS query has to traverse the full sequence from the Root Name Server down to the Authoritative Name Server. To reduce repetitive queries and cut down response times, the DNS system utilizes a critical mechanism known as DNS Cache.

DNS Cache (DNS buffer memory) is a mechanism that temporarily stores the results of domain-to-IP resolutions for a designated duration determined by TTL (Time To Live). As long as the TTL remains valid, the system reuses the cached result instead of executing a new DNS query.

DNS Cache can reside at multiple layers throughout Internet access, including:

- Web browsers: Browsers frequently store a DNS Cache to expedite repetitive visits. When a user reopens a previously visited website, the browser can immediately use the cached DNS information without dispatching an outbound request.

- Operating systems: The operating system serves as the intermediary between browsers and the Internet network. A DNS Cache at the OS level allows multiple applications on the same device to share resolution outcomes, thereby reducing generated queries.

- ISP DNS Servers: DNS Servers operated by Internet Service Providers (ISPs) also maintain DNS Caches to serve numerous concurrent users. As a result, popular queries can be answered rapidly without having to escalate to higher-tier DNS servers.

Thanks to the DNS Cache mechanism, DNS queries do not need to repeat from scratch for every single visit, reducing latency, conserving network resources, and substantially improving website loading speeds for end users.

Common DNS records today

Within the DNS framework, every domain name is managed via DNS records. Each record type fulfills a distinct function, helping route traffic, run services, and guarantee website stability.

- A Record: The A Record is used to point a domain or subdomain to a specific IPv4 address. This is the foundational and most widely utilized record for connecting a domain name to a web hosting server.

- AAAA Record: The AAAA Record performs a function similar to the A Record, but points the domain name to an IPv6 address, accommodating future expansions of the Internet address space.

- CNAME Record: The CNAME Record allows the creation of an alias pointing to another domain name. Instead of pointing directly to an IP address, CNAME points to a canonical domain name, making configuration management and updates far more flexible.

- MX Record: The MX Record defines the mail servers responsible for handling email for the domain name. This record enables administrators to specify multiple mail servers along with priority levels to guarantee reliable email dispatch and delivery.

- TXT Record: The TXT Record holds text-based information and is commonly utilized for domain verification, security configurations, or establishing policies associated with email and third-party services.

- NS Record: The NS Record specifies the authoritative DNS servers that manage the domain name. This record informs the DNS system which server must be queried when resolving the domain name.

Proper and complete configuration of DNS records ensures that the Domain Name System operates accurately and stably, serving as a critical foundation for websites, email, and Internet services to run efficiently.

Why is DNS a crucial component of the Internet?

DNS is considered a core pillar of the Internet, functioning as an essential bridge between users and online services. Before a website can load, an email can be delivered, or an application can connect to a server, the DNS infrastructure is always an indispensable first step.

Page load speed

DNS directly impacts the initial response time when users access a website. A well-architected and optimized DNS infrastructure ensures that domain name resolution happens swiftly, minimizing latency before the browser begins rendering content. Conversely, sluggish DNS responses can cause websites to "freeze," even if the destination web server is operating normally.

System stability

DNS plays a vital role in ensuring continuous access to websites and online services. When a server or network path experiences an outage, DNS can reroute traffic to alternate backup servers, minimizing downtime and maintaining overall system availability.

Service routing capabilities

DNS does not merely return a static IP address; it can also execute intelligent traffic routing. Based on the user's geographic location, current system load, or the specific service requested, DNS helps direct users to the most suitable server. This mechanism serves as the underlying backbone for modern architectures such as CDNs, cloud infrastructure, and global content delivery platforms.

Information security level

DNS plays an instrumental role in safeguarding users and systems against cyber threats. Through authentication mechanisms, query inspection, and anomaly detection, DNS helps mitigate risks like domain spoofing, malicious redirection, and phishing attacks, thereby elevating safety across Internet interactions.

A single disruption involving DNS can render a website completely unreachable even while the origin server remains fully functional, underscoring that DNS is a pivotal link determining the performance, stability, and security of the entire Internet ecosystem.

While DNS helps mitigate a portion of spoofing and malicious redirection risks, achieving comprehensive protection against attacks targeting websites and web applications is essential. 

Frequently Asked Questions

What is DNS and what is it used for?

DNS is the domain name resolution system that converts website names into IP addresses so computers can connect to the correct server. Thanks to DNS, users do not need to memorize complex numeric IP strings when accessing the Internet.

How does a DNS Server differ from a web server?

A DNS Server is solely responsible for resolving domain names, whereas a web server hosts the actual website content. DNS helps browsers find the correct web server prior to retrieving and rendering data for users.

Does the Domain Name System affect website speed?

Yes. DNS affects the initial query lookup time when users visit a website. A DNS system that runs reliably and features robust caching mechanisms will reduce latency and improve overall page load performance.

What is DNS Cache?

DNS Cache is temporary storage that retains DNS resolution results for a set period. Thanks to DNS Cache, subsequent visits do not need to re-query the entire DNS hierarchy, resulting in faster access.

What happens if DNS experiences an outage?

When DNS experiences an issue, users may be unable to access the website even if the hosting server remains fully functional. The browser simply cannot resolve the corresponding IP address for the entered domain name.

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