Knowledge Base

The internet has become an indispensable part of today's world. Many activities, from accessing websites to sending emails, from online games to video conferences, are carried out over the internet. A complex system works in the background of these processes. An important part of this system is the Domain Name System (DNS). DNS is a system that translates internet addresses (e.g., www.example.com) into IP addresses (e.g., 192.0.2.1). The DNS cache is a mechanism used to speed up this translation process. In this article, we will examine in detail what the DNS cache is, how it works, why it needs to be cleared, and how to clear the DNS cache on different operating systems.

1. What is DNS and How Does it Work?

1.1. The Basic Function of DNS

DNS is like the phone book of the internet. It converts domain names that people can easily remember (e.g., google.com) into IP addresses that machines can understand (e.g., 142.250.185.142). In this way, when you want to access a website, your browser first contacts DNS servers to find out the IP address of the relevant domain name and then connects to the website via this IP address.

1.2. DNS Query Process

The DNS query process that takes place when you want to access a website consists of the following steps:

1. Your browser checks whether the IP address of the relevant domain name exists in your operating system's DNS cache. If it exists, it connects to the website directly using this IP address.
2. If it does not exist in the cache, your operating system sends a DNS query to the configured DNS server (usually your internet service provider's (ISP) DNS server).
3. The DNS server checks whether the IP address of the relevant domain name exists in its own cache. If it exists, it sends this IP address back to your browser.
4. If it does not exist in the DNS server's cache either, it contacts the root DNS servers. The root servers specify which top-level domain (TLD, e.g., .com, .org, .net) DNS server the domain name is located on.
5. The DNS server contacts the relevant TLD DNS server to find out the address of the authoritative DNS server.
6. The DNS server contacts the authoritative DNS server to find out the IP address of the relevant domain name.
7. The authoritative DNS server sends the IP address of the domain name back to the DNS server.
8. The DNS server sends the IP address back to your browser and also saves it to its own cache.
9. Your browser connects to the website using the IP address.

Although this process may seem complex at first glance, it is a fundamental mechanism that ensures the smooth operation of the internet.

1.3. DNS Record Types

There are different types of records in DNS. The most commonly used record types are:

• A Record: Maps a domain name to an IPv4 address.
• AAAA Record: Maps a domain name to an IPv6 address.
• CNAME Record: Redirects a domain name to another domain name.
• MX Record: Specifies the mail server for a domain name.
• TXT Record: Contains text-based information about a domain name.
• NS Record: Specifies the DNS servers for a domain name.

2. What is DNS Cache?

2.1. Purpose and Function of Cache

DNS cache is a mechanism used to speed up the DNS querying process. DNS servers and operating systems store the IP addresses of previously queried domain names in the cache for a certain period. This allows faster connection to the website by using the information in the cache instead of sending queries to DNS servers again when the same domain name is accessed again.

2.2. Cache Types: Local and Remote

DNS cache can be of two basic types:

• Local DNS Cache: The cache stored on your operating system (Windows, macOS, Linux) or in your browser (Chrome, Firefox, Safari).
• Remote DNS Cache: The cache held by your Internet Service Provider (ISP) or public DNS servers (e.g., Google DNS, Cloudflare DNS).

2.3. TTL (Time To Live) Value

Each DNS record has a TTL (Time To Live) value. TTL specifies how long the DNS record will be stored in the cache. The TTL value is expressed in seconds. For example, if the TTL value of a DNS record is 3600 seconds (1 hour), this record is stored in the cache for 1 hour. After the TTL expires, a query is sent to the DNS servers again to check if the DNS record is up to date.

3. Why Should DNS Cache Be Cleared?

3.1. Incorrect or Outdated DNS Records

Sometimes, the IP address of a website may change. In this case, if the old IP address is stored in your DNS cache, you may experience problems accessing the website. Clearing the DNS cache can solve this problem by ensuring that the current IP address is obtained.

3.2. Security Risks and Cache Poisoning

DNS cache poisoning is a situation where malicious people inject incorrect or harmful DNS records into the cache of DNS servers. In this case, users may be directed to fake websites and their personal information may be stolen. Regularly clearing the DNS cache can help reduce these types of security risks.

3.3. Connection Problems and Error Messages

Incorrect or corrupted records in the DNS cache can cause connection problems or error messages when accessing websites. Clearing the DNS cache can help resolve these types of issues.

4. DNS Cache Clearing Methods

4.1. Clearing DNS Cache in Windows

4.1.1. Using Command Prompt

The most common way to clear the DNS cache in Windows is to use the Command Prompt. Here are the step-by-step instructions:

1. Open Command Prompt as an administrator. To do this, type "cmd" in the Start menu, right-click on Command Prompt, and select "Run as administrator".
2. Type the following command into the Command Prompt and press Enter:

   ipconfig /flushdns

3. When the command is completed successfully, you will see a message that says "Successfully flushed the DNS Resolver Cache".

4.1.2. Using PowerShell

PowerShell can also be used to clear the DNS cache. Here are the step-by-step instructions:

1. Open PowerShell as an administrator. To do this, type "powershell" in the Start menu, right-click on PowerShell, and select "Run as administrator".
2. Type the following command into PowerShell and press Enter:

   Clear-DnsClientCache

3. When the command is completed successfully, you may not see any message.

4.2. Clearing DNS Cache on macOS

The command to clear the DNS cache on macOS varies depending on the macOS version. Below are the commands for different macOS versions:

4.2.1. macOS Sierra (10.12) and Later

1. Open the Terminal application.
2. Type the following command and press Enter:

   sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

3. Enter your password and press Enter.

4.2.2. macOS Yosemite (10.10) and El Capitan (10.11)

1. Open the Terminal application.
2. Type the following command and press Enter:

   sudo discoveryutil mdnsflushcache; sudo discoveryutil udnsflushcaches

3. Enter your password and press Enter.

4.2.3. macOS Mavericks (10.9)

1. Open the Terminal application.
2. Type the following command and press Enter:

   sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

3. Enter your password and press Enter.

4.2.4. macOS Lion (10.7) and Mountain Lion (10.8)

1. Open the Terminal application.
2. Type the following command and press Enter:

   sudo killall -HUP mDNSResponder

3. Enter your password and press Enter.

4.3. Clearing DNS Cache on Linux

The method to clear the DNS cache on Linux varies depending on the DNS resolver used. The most commonly used DNS resolvers are:

• systemd-resolved: Used by default in most modern Linux distributions.
• nscd (Name Service Cache Daemon): Commonly used in older systems.
• dnsmasq: Often used as a DNS and DHCP server in local networks.

4.3.1. Using systemd-resolved

1. Open the terminal application.
2. Type the following command and press Enter:

   sudo systemd-resolve --flush-caches

3. If necessary, enter your password and press Enter.

4.3.2. Using nscd

1. Open the terminal application.
2. Type the following command and press Enter:

   sudo service nscd restart

   Or:

   sudo /etc/init.d/nscd restart

3. If necessary, enter your password and press Enter.

4.3.3. Using dnsmasq

1. Open the terminal application.
2. Type the following command and press Enter:

   sudo service dnsmasq restart

   Or:

   sudo /etc/init.d/dnsmasq restart

3. If necessary, enter your password and press Enter.

4.4. Clearing DNS Cache in Browser

Some browsers also keep their own DNS caches. To clear your browser's DNS cache, you can follow these steps:

4.4.1. Google Chrome

1. Type "chrome://net-internals/#dns" in the Chrome address bar and press Enter.
2. Click the "Clear host cache" button.

4.4.2. Mozilla Firefox

Firefox does not have its own DNS cache mechanism. It usually uses the operating system's DNS cache.

4.4.3. Microsoft Edge

1. Type "edge://net-internals/#dns" in the Edge address bar and press Enter.
2. Click the "Clear host cache" button.

5. Changing DNS Servers

5.1. Why Change DNS Servers?

By default, you use your internet service provider's (ISP) DNS servers. However, your ISP's DNS servers may be slow or unreliable. You can improve your internet experience by using faster and more reliable DNS servers. Additionally, some DNS servers offer additional security features and can block access to malicious websites.

5.2. Popular DNS Servers

Some of the most popular DNS servers include:

• Google Public DNS: 8.8.8.8 and 8.8.4.4
• Cloudflare DNS: 1.1.1.1 and 1.0.0.1
• OpenDNS: 208.67.222.222 and 208.67.220.220

5.3. Steps to Change DNS Servers

5.3.1. Changing DNS Servers on Windows

1. Open the Control Panel.
2. Click on "Network and Internet".
3. Click on "Network and Sharing Center".
4. Click on "Change adapter settings".
5. Right-click on your active network connection (Ethernet or Wi-Fi) and select "Properties".
6. Select "Internet Protocol Version 4 (TCP/IPv4)" and click the "Properties" button.
7. Select "Use the following DNS server addresses".
8. Enter the addresses of your preferred DNS servers in the "Preferred DNS server" and "Alternate DNS server" fields. For example, for Google Public DNS, you can enter 8.8.8.8 and 8.8.4.4.
9. Click the "OK" button.
10. Repeat the same steps for "Internet Protocol Version 6 (TCP/IPv6)".

5.3.2. Changing DNS Servers on macOS

1. From the Apple menu, select "System Preferences".
2. Click on "Network".
3. Select your active network connection (Ethernet or Wi-Fi).
4. Click the "Advanced" button.
5. Select the "DNS" tab.
6. Click the "-" button to delete the existing DNS servers.
7. Click the "+" button to add new DNS servers and enter the addresses of your preferred DNS servers. For example, for Google Public DNS, you can enter 8.8.8.8 and 8.8.4.4.
8. Click the "OK" button.
9. Click the "Apply" button.

5.3.3. Changing DNS Servers on Linux

The method for changing DNS servers on Linux varies depending on the network manager used. The most commonly used network managers are:

• NetworkManager: Used by default in most desktop Linux distributions.
• systemd-networkd: Commonly used in server systems.

If you are using NetworkManager, you can follow these steps:

1. Click on the network manager icon.
2. Select your active network connection (Ethernet or Wi-Fi).
3. Click on "Edit Connections" or a similar option.
4. Select the "IPv4 Settings" or "IPv6 Settings" tab.
5. In the "DNS" field, enter the addresses of your preferred DNS servers, separated by commas. For example, for Google Public DNS, you can enter 8.8.8.8, 8.8.4.4.
6. Click the "Save" button.

If you are using systemd-networkd, you need to edit the network configuration file. This file is usually located in the `/etc/systemd/network/` directory. After editing the file, you need to restart the network service.

6. Real-Life Examples and Case Studies

6.1. Website Unavailability Situation

A user was constantly receiving error messages when trying to access their favorite website. Despite trying different browsers, the result remained the same. The user was sure that their internet connection was stable. While investigating the source of the problem, they realized that the DNS cache was not up to date. After clearing the DNS cache, they were able to access the website without any issues.

6.2. Slow Internet Connection Issue

A company noticed that their internet connection was slow and accessing websites took a long time. The system administrator checked the performance of the DNS servers and found that the ISP's DNS servers were running slowly. After switching to faster DNS servers such as Google Public DNS or Cloudflare DNS, the internet connection significantly improved.

6.3. Security Breach Case

A user noticed that when trying to access their bank's website, they were redirected to a fake website. The fake website looked very similar to the bank's website, and the user entered their login information. Later, they noticed unauthorized withdrawals from their bank account. As a result of the investigations, it was determined that the user's DNS cache had been poisoned and they were redirected to the fake website. This case highlights the importance of clearing the DNS cache and using reliable DNS servers.

7. Frequently Asked Questions (FAQ) About DNS

7.1. How often should the DNS cache be cleared?

You do not need to clear the DNS cache regularly. Usually, it is sufficient to clear the DNS cache when you have trouble accessing websites or after IP address changes. However, you can clear the DNS cache once or twice a month to reduce security risks.

7.2. Does clearing the DNS cache increase my internet speed?

Clearing the DNS cache does not directly increase your internet speed. However, if you are experiencing problems accessing websites due to incorrect or outdated records in the DNS cache, clearing the DNS cache can resolve these issues and allow you to access websites faster.

7.3. Which DNS servers should I use?

You can use popular and reliable DNS servers such as Google Public DNS (8.8.8.8 and 8.8.4.4), Cloudflare DNS (1.1.1.1 and 1.0.0.1), and OpenDNS (208.67.222.222 and 208.67.220.220). These DNS servers are generally faster and more reliable than your ISP's DNS servers.

7.4. What is DNSSEC?

DNSSEC (Domain Name System Security Extensions) is a set of extensions that adds a security layer to the DNS protocol. DNSSEC ensures the integrity and authenticity of DNS records. This provides protection against attacks such as DNS cache poisoning.

7.5. What is DNS leak?

A DNS leak is when your DNS queries are sent unencrypted to your ISP while using a VPN or proxy. This can compromise your privacy. By performing DNS leak tests, you can check whether your VPN or proxy provides protection against DNS leaks.

8. Conclusion and Summary

DNS caching is an important mechanism that speeds up the internet experience. However, incorrect or outdated DNS records can cause security risks and connection problems. Therefore, it is important to regularly clear the DNS cache and use reliable DNS servers. In this article, we have examined in detail what DNS is, how DNS caching works, why it needs to be cleared, and how to clear the DNS cache on different operating systems. I hope this information helps you improve your internet experience.

Key Points:

• DNS is a system that translates internet addresses into IP addresses.
• DNS caching is used to speed up the DNS query process.
• DNS cache can be of two types: local (operating system, browser) and remote (ISP, public DNS servers).
• DNS caching can cause incorrect or outdated records, security risks, and connection problems.
• The DNS cache can be cleared using different commands in Windows, macOS, and Linux.
• You can improve your internet experience by using reliable DNS servers.