What is DNS? Detailed Guide on Domain Name System

DNS stands for Domain Name System. It is a crucial component of the Internet that translates human-readable domain names into machine-readable IP addresses.

In this article, we have provided an in-depth explanation of the Domain Name System (DNS). This guide will help you learn the working of DNS and DNS servers, and their applications.

Furthermore, if you are a networking professional and want to gain a better understanding of DNS and its troubleshooting, you can also enroll in a networking courses.

What is Domain Name System (DNS)?

DNS is a service that converts human-readable domain names (like www.example.com) into machine-readable IP addresses (such as 192.0.2.1). It eliminates the need for users to remember complex numerical addresses, simplifies web browsing, and enhances overall internet functionality.

The Domain Name System utilizes various DNS servers to store and manage these translations efficiently.

What is a DNS Server?

A DNS server is a specialized computer equipped with a database that maps domain names to their associated public IP addresses.

When users type a domain name, such as `Fortinet.com` or `Yahoo.com`, into their browser’s address bar, the DNS server retrieves the appropriate IP address for these domains and automatically guides the user’s device to the correct location where the requested website's data is stored.

Once the DNS server identifies the right IP address, web browsers utilize this information to send data requests to the Content Delivery Network (CDN) edge servers or origin servers.

This process begins with the DNS server finding the IP address linked to a website's URL.

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Role of DNS in Internet Communication

DNS is essential for connecting users with websites. Without it, users would need to remember the IP addresses of all the sites they visit.

The DNS server simplifies this process, allowing users to type in a familiar name, which the server then converts into the appropriate IP address. For example, when a user enters `www.fortinet.com`, the DNS server identifies the corresponding IP address and directs the browser to the correct site.

Types of DNS Servers

A typical DNS query involves a series of interactions between four types of DNS servers to provide the necessary IP address:

1. DNS Recursor

Also known as a DNS resolver, this server receives the initial query from the user’s device. It communicates with other DNS servers to find the correct IP address. Acting as a client, the resolver sends queries to the other three types of DNS servers: root nameservers, top-level domain (TLD) nameservers, and authoritative nameservers.

2. Root Nameservers

These servers are responsible for the Internet's DNS root zone. They respond to requests by providing a list of authoritative nameservers that correspond to the correct TLD.

3. TLD Nameservers

A TLD nameserver stores the IP addresses associated with second-level domains within the TLD. It responds to queries by supplying the IP address of the requested website and forwards the query to the domain's nameserver.

4. Authoritative Nameservers

These servers provide the definitive answer to the DNS query. There are two types: master (or primary) nameservers, which maintain the original copies of zone records, and slave (or secondary) nameservers, which replicate the master server's records and provide backup. They share the load of DNS queries and ensure availability.

How DNS Work?

Here’s a step-by-step breakdown of how DNS works:

Step 1. User Request

When a user types a URL into a web browser, the browser first checks if it already has the IP address cached. If not, it initiates a DNS query to resolve the domain name.

Step 2. Recursive DNS Resolver

The request goes to a recursive resolver, usually provided by the user’s Internet Service Provider (ISP). The resolver's job is to find the IP address associated with the domain name, beginning with the root of the DNS hierarchy.

Step 3. Root Name Servers

If the recursive resolver doesn’t have the domain’s IP cached, it queries a root name server. Root name servers manage information for the top-level domains (TLDs) like `.com`, `.org`, or `.net`, and direct the resolver to the appropriate TLD name server for the domain requested.

Step 4. Top-Level Domain (TLD) Name Servers

The resolver then queries the TLD name server, which holds information for the specific domain suffix (e.g., `.com`). The TLD server directs the resolver to the authoritative name server for the domain.

Step 5. Authoritative Name Server

The authoritative name server holds the DNS records for the specific domain (e.g., `example.com`) and provides the IP address associated with the domain. This response is then returned to the recursive resolver.

Step 6. Returning the IP to the User’s Browser

The recursive resolver sends the IP address back to the user’s device, which uses it to initiate a connection to the web server associated with that IP. The web server then responds, and the user sees the website.

Step 7. Caching the Result

Both the recursive resolver and the user’s device typically cache the DNS response for a specified period (known as the Time to Live or TTL), making future requests for the same domain faster by avoiding the full resolution process.

DNS Record Types

The database in a DNS server stores various kinds of data. These data entries help in the working of DNS. Some DNS record types are:

• ● A (Address) Records: Maps a domain name to an IPv4 address.


• ● AAAA Records: Maps a domain name to an IPv6 address.


• ● CNAME (Canonical Name) Records: Aliases one domain name to another.


• ● MX (Mail Exchange) Records: Specifies mail servers for a domain.


• ● TXT Records: Hold arbitrary text data, often used for security (e.g., SPF, DKIM records).


• ● NS (Name Server) Records: Lists the authoritative name servers for a domain.

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Authoritative vs. Recursive DNS Servers

The distinction between authoritative DNS servers and recursive DNS servers is significant. Authoritative nameservers store DNS records and respond directly to queries about specific domain names. In contrast, recursive servers act as intermediaries between the user and the authoritative servers, navigating the DNS hierarchy to retrieve the necessary records.

The table below compares Authoritative vs Recursive DNS Servers and lists major differences between them.

DNS Server Error: What Does “DNS Server Not Responding” Mean?

Occasionally, users may encounter a message stating that the "DNS server isn’t responding" after entering a domain name. This indicates that the attempt to communicate with the DNS server failed.

Possible causes include:

• ● An unstable or weak internet connection, hindering communication with the DNS server.


• ● Outdated DNS settings or browser configurations.


• ● Issues with the DNS server itself, such as power outages at its data center.

Popular DNS Servers

Several notable DNS services are available, each offering unique features:

1. 1. Cloudflare (1.1.1.1): Known for its user-friendly setup, Cloudflare provides tutorials for various operating systems and includes options for blocking adult content.


2. 2. Google Public DNS: Designed for more technical users, Google’s DNS service also provides guidance for setup.


3. 3. Quad9: Renowned for its speed, Quad9’s service also utilizes threat intelligence to block access to malicious sites.

Also Check: Popular Cloud Service Providers.

What is DNS Caching?

Caching is a technique used by both operating systems and browsers to store DNS resource records. This process reduces redundancy by eliminating the need to repeatedly query the DNS server for the same information. If a device recently accessed a website, the IP address can be retrieved from its cache, speeding up the connection process.

OS DNS Caching

Most operating systems can maintain a local copy of DNS lookups, enabling quick access to necessary information for resolving URLs to their respective IP addresses.

What is DNS Cache Poisoning?

DNS cache poisoning, also known as DNS spoofing, is a security vulnerability where corrupt DNS data is inserted into a resolver’s cache. This can lead to users being directed to malicious websites instead of the intended sites.

How to Perform a DNS Lookup?

Each domain has associated DNS records that can be accessed via nameservers. Users can check the status of these records using tools like the NSLOOKUP command on Windows.

To perform a DNS lookup:

1. Step 1. Open the Windows command prompt (Start > Command Prompt or Run > CMD).


2. Step 2. Type `NSLOOKUP` and hit Enter; this sets the default server to your local DNS.


3. Step 3. Specify the type of DNS record by entering `set type=`, where `` represents the desired record type (e.g., A, AAAA, CNAME).


4. Step 4. Enter the domain name you wish to query and press Enter.


5. Step 5. The NSLOOKUP command will return the record entries for the specified domain.

DNS Queries

During the DNS lookup process, three types of queries can be executed to optimize the resolution of DNS requests:

• ● Recursive Query: The resolver must obtain the complete answer to the query.


• ● Iterative Query: The resolver may receive a referral to another server instead of a complete answer.


• ● Non-recursive Query: The resolver provides an answer from its cache.



Free vs Paid DNS Servers

While many users may find free DNS servers sufficient, premium services offer numerous advantages, including:

● Dynamic DNS (DDNS): This service allows remote access to home computers by mapping changing IP addresses to a domain name.

● Secondary DNS: Provides backup to ensure domain availability during outages.

● Management Interface: Paid services often include user-friendly dashboards for easy management.

● Enhanced Security: Paid DNS services typically offer additional security features.

● Performance Guarantees: Premium services come with service-level agreements (SLAs) that ensure high DNS resolution rates.

● Customer Support: Paid services usually provide dedicated customer support for troubleshooting and inquiries.

Conclusion

In conclusion, the Domain Name System is a foundational element of the Internet, simplifying navigation and communication.

By transforming user-friendly domain names into IP addresses, DNS servers enable seamless access to online resources, enhancing the overall user experience.

Understanding DNS's functionality and structure is essential for anyone involved in network management or internet usage.