What is DNS?

An article about what DNS is and how DNS works.

What is DNS?

The meaning of DNS is Domain Name System, is a critical component of the internet infrastructure that translates human-friendly domain names into IP addresses, which are machine-readable. This system allows users to access websites using easy-to-remember domain names instead of complex numerical IP addresses. DNS operates much like a phone book for the internet, where upon entering a domain name, such as www.example.com, the DNS system translates this into the corresponding IP address, such as This process is crucial for facilitating communication between different devices over the internet.

5 DNS Services Involved in Loading a Webpage

There are several types of DNS services, each serving a unique purpose:

  1. DNS Resolver: This is the first stop in the DNS lookup process. It receives the query from the client and then interacts with other DNS servers to find the correct IP address.
  2. Recursive DNS Servers: These servers take DNS queries from DNS resolvers and search for the answer. If they don't have the answer, they query other servers, including root, TLD, and authoritative DNS servers.
  3. Root DNS Servers: These servers direct queries to the appropriate Top-Level Domain (TLD) servers.
  4. TLD DNS Servers: These servers store information about domains based on their extensions, such as .com, .org, .net, etc.
  5. Authoritative DNS Servers: These servers store DNS record information, including the IP address for a specific domain name.

How Does DNS Work?

Imagine you're in a city where you don't know your way around, and you need to find a specific address. You'd probably use a map or a GPS system. The DNS works similarly for the internet. When you type a website address into your browser, the DNS system starts a search for the corresponding IP address.

This process, known as a DNS lookup, involves several steps:

  1. The user enters a URL into a web browser.
  2. The query first checks the local cache of the operating system; if the domain name is found, the process ends here, and the IP address is returned.
  3. If the domain name is not in the local cache, the query is sent to the DNS resolver configured in the system settings, which is usually a local DNS server provided by the internet service provider (ISP).
  4. The local DNS server checks its cache to see if it has a record of the IP address for the domain name. If it does, it returns the IP address to the DNS resolver, and the process ends.
  5. If the local DNS server doesn't have the information cached, it acts as a recursive DNS server and sends a query to the root DNS server.
  6. The root server responds with a pointer to the TLD (Top-Level Domain) server.
  7. The local DNS server then sends a query to the TLD server, which responds with a pointer to the authoritative DNS server.
  8. The local DNS server sends a query to the authoritative server, which responds with the IP address for the domain name.
  9. The local DNS server sends the IP address back to the DNS resolver, caching the record for future queries.
  10. The DNS resolver provides the IP address to the web browser, which then requests the web page from the web server associated with that IP address.
  11. The web server sends the web page back to the web browser for the user to view.

What are the Types of DNS Queries?

In a typical DNS lookup three types of queries occur. By using a combination of these queries, an optimized process for DNS resolution can result in a reduction of distance traveled.

  1. Recursive Query: In a recursive query, the DNS client requires the DNS server to respond with either the requested resource record or an error message if the DNS server cannot find the record. If the DNS server does not have the information in its cache, it will query other DNS servers on behalf of the client until it finds the information or confirms that the information does not exist.
  2. Iterative Query: In an iterative query, the DNS client allows the DNS server to return the best answer it can give based on its current cache. If the queried DNS server does not have the exact match, it will return a referral to other DNS servers. The client then queries these other servers.
  3. Non-Recursive Query: Non-recursive queries are typically used by DNS servers to communicate with each other. The DNS client (usually another DNS server) will ask the server for a record and the server will respond with the record or say it does not have it. Unlike recursive queries, the server will not go out of its way to find the record.

Why is the DNS Server not Responding?

You may get a message that says "DNS server isn't responding" after entering a domain name in the URL bar of your browser. This means there was an attempt to communicate with the DNS server, but the server failed to return a result. Here are a few possible causes:

  1. Network Issues: The most common reason is network connectivity issues. This could be due to problems with your Internet Service Provider (ISP), your local network, or your personal device's connection.
  2. Server Downtime: The DNS server itself might be temporarily down or overloaded with requests. This can happen if the server is experiencing high traffic or undergoing maintenance.
  3. Incorrect DNS Settings: If the DNS settings on your device or router are incorrect, it could prevent the DNS server from responding. This could be due to incorrect DNS addresses or other configuration errors.
  4. DNS Cache Issues: Sometimes, the information stored in your DNS cache might be outdated or corrupt, which can cause issues.

What is DNS Propagation?

DNS propagation is a crucial concept in the world of networking and the internet. It refers to the time taken for all the servers across the globe to update their records with new DNS (Domain Name System) information. When a change is made to a domain's DNS records, such as modifying the IP address of a website or migrating to a new host, this information needs to be updated on all DNS servers worldwide. This process is what we refer to as DNS propagation.

The duration of DNS propagation can vary significantly, typically ranging from a few minutes to 48 hours or more. This variation is due to the different update frequencies of Internet Service Providers (ISPs). Some ISPs refresh their DNS records more frequently than others, leading to quicker updates for some users.

During the propagation period, some users might still be directed to your old site or IP address until their ISP updates their DNS records. This is why you might experience some downtime or inconsistencies when you make significant changes to your DNS records.

One of the key factors influencing DNS propagation time is the TTL (Time To Live) setting in your DNS records. TTL is a value that determines how long a DNS record is kept in the cache of DNS servers and user's computers. A lower TTL means the record will expire sooner, prompting servers to fetch the updated information more quickly. Therefore, if you're planning to change DNS records, you can reduce the TTL value ahead of time to potentially decrease propagation time.

However, even with a low TTL, you may still encounter issues if old DNS information is stored in your local DNS cache. This is where the concept of 'flush DNS' comes into play. Flush DNS is the process of clearing out old DNS information from your local cache, forcing your computer to retrieve the latest DNS information.

What is Reverse DNS Lookup?

Reverse DNS lookup, also known as rDNS lookup, is a process that finds the hostname associated with a specific IP address. It's the opposite of the more common forward DNS lookup, which locates an IP address based on a hostname.

In a forward DNS lookup, your computer consults a DNS server to find the IP address for a specific domain name or hostname. For instance, if you enter "www.example.com" into your web browser, your computer will perform a forward DNS lookup to find the IP address associated with that domain name.

In a reverse DNS lookup, the process is flipped. Your computer starts with an IP address and uses a DNS server to find the associated hostname. This is often used for troubleshooting, verifying the authenticity of devices, and in certain security scenarios.

To perform a reverse DNS lookup, you can use various online tools or command-line utilities. For example, on a Unix-based system like Linux or macOS, you can use the "dig" command with the "-x" option followed by the IP address. On Windows, you can use the "nslookup" command followed by the IP address.

It's important to note that not all IP addresses will have a corresponding hostname, as not all IP owners choose to set up reverse DNS records.

What is DNS Filtering?

DNS filtering is a technique used to control or restrict access to certain websites or online content. It works by blocking or allowing data packets based on the domain names they are associated with.

Here's how it works: When you type a URL into your web browser, your computer uses the Domain Name System (DNS) to translate that URL into an IP address that it can understand. This process is known as a DNS lookup.

DNS filtering takes place during this lookup process. When a request is made to a DNS server to resolve a domain name, the DNS filter checks the request against a database of blocked or allowed websites. If the website is on the blocked list, the DNS server will return an 'error' or redirect to a different page, effectively blocking access to the website. If the website is not on the blocked list, the DNS server will resolve the domain name as usual, allowing access.

DNS filtering is commonly used in businesses and schools to prevent access to inappropriate or harmful content. It can also be used to block access to known malicious websites, helping to protect users from phishing attacks and malware.

Advantages of Tencent EdgeOne DNS Services

Tencent EdgeOne DNS services, brings several advantages to the table:

  1. Global Coverage: EdgeOne DNS service has a globally distributed network of nodes, ensuring that users can quickly resolve to the nearest server, providing faster access speeds no matter where they are.
  2. High Availability: EdgeOne DNS service is designed for high availability. Even if a node encounters an issue, it can automatically switch to other nodes to ensure service stability.
  3. DDoS Protection: EdgeOne DNS service provides DDoS protection capabilities, effectively defending against large-scale DDoS attacks and protecting your website from such threats.
  4. Intelligent Resolution: EdgeOne DNS service supports intelligent resolution. It can automatically resolve to the optimal server based on factors such as the user's geographical location and network conditions, providing a better user experience.
  5. Ease of Use: EdgeOne DNS service provides an easy-to-use management interface. You can conveniently manage your DNS records without needing specialized technical knowledge.
  6. Security: EdgeOne DNS service provides various security measures, including DNSSEC (DNS Security Extensions), to protect your DNS records from being tampered with.

These advantages make Tencent EdgeOne DNS service an efficient, reliable, and secure DNS solution. You are welcome to Contact Us for more information.