How To Flush The Dns | Clear Your Cache

Understanding how your computer resolves domain names into IP addresses is a fundamental concept in networking, much like learning how a library catalog helps you find a specific book. Sometimes, this local “catalog” needs a refresh to ensure you’re always getting the most current information available on the internet. This process, known as flushing the DNS, can resolve various connectivity and browsing issues by clearing out stale or incorrect entries.

Understanding the Domain Name System (DNS)

The Domain Name System, or DNS, functions as the internet’s phonebook. When you type a website address like “example.com” into your browser, DNS translates that human-readable domain name into a machine-readable Internet Protocol (IP) address, such as 192.0.2.1. This translation is essential because computers communicate using numerical IP addresses, not domain names.

This system operates through a hierarchical and distributed network of servers. When your computer needs to find an IP address for a domain, it queries these servers, starting with local caches and moving up to root servers if necessary. The process ensures efficient and reliable access to web resources globally.

The Local DNS Cache: A Performance Enhancer

To speed up web browsing and reduce the load on DNS servers, your operating system and web browsers maintain a local DNS cache. This cache stores recently resolved domain names and their corresponding IP addresses. When you revisit a website, your computer first checks its local cache. If the entry is found, it retrieves the IP address directly, bypassing the need to query external DNS servers. This significantly reduces latency and improves loading times.

Each entry in the DNS cache has a Time To Live (TTL) value, which dictates how long the record should be considered valid. Once the TTL expires, the entry is marked as stale, and the system will request a new resolution the next time that domain is accessed. This mechanism helps ensure that cached information remains relatively current.

When to Flush Your DNS Cache

While the DNS cache is beneficial for performance, there are specific scenarios where it can become a hindrance, necessitating a flush. Clearing the cache ensures your system retrieves the most current DNS records, resolving potential issues.

• Website Not Loading or Displaying Incorrectly: If a website has recently moved to a new server with a different IP address, your local cache might still hold the old, incorrect IP. Flushing the cache forces your system to fetch the updated record.
• Accessing Newly Registered Domains: For very new domains, DNS propagation across the internet can take some time. If you’re trying to access a site that just went live, flushing your cache might help you resolve it faster once the global DNS records are updated.
• Troubleshooting Network Connectivity Issues: Persistent issues with accessing certain websites or network services can sometimes stem from corrupted or outdated DNS cache entries. A flush can be a valuable diagnostic step.
• After Changing DNS Servers: If you manually change your computer’s DNS server settings (e.g., from your ISP’s default to a public DNS like Google DNS or Cloudflare DNS), flushing the cache ensures your system immediately starts using the new servers for all future resolutions.
• Security and Privacy Concerns: In rare cases, malicious software might tamper with your DNS cache to redirect you to fraudulent websites (DNS spoofing). Flushing the cache can help clear such malicious entries.

The Domain Name System is a foundational internet service, managed by organizations like the Internet Corporation for Assigned Names and Numbers (ICANN), which coordinates its global operation.

Scenario	Potential Cause	Benefit of Flushing DNS
Website inaccessible	Stale IP address in cache	Forces resolution of current IP
Slow website loading	Corrupted cache entry	Removes problematic data
New DNS server not active	Old server entries persist	Activates new server immediately

How to Flush DNS on Windows

Flushing the DNS cache on a Windows operating system involves using the Command Prompt. This process clears the resolver cache, ensuring that subsequent DNS queries are sent to your configured DNS servers.

Using Command Prompt for Windows

1. Open Command Prompt as Administrator:
   • Click the Start button.
   • Type “cmd” in the search bar.
   • Right-click on “Command Prompt” in the search results.
   • Select “Run as administrator.” You will need to confirm the User Account Control prompt.
2. Execute the Flush Command:
   • In the Command Prompt window, type the following command and press Enter:

     ipconfig /flushdns

   • You should see a confirmation message stating, “Successfully flushed the DNS Resolver Cache.”
3. Optional: Register New DNS and Display Cache:
   • To register your computer’s DNS entries, you can use:

     ipconfig /registerdns

   • To view the current contents of your DNS resolver cache (before or after flushing), use:

     ipconfig /displaydns

This command specifically clears the DNS resolver cache maintained by the Windows operating system, which is distinct from any DNS caches maintained by individual web browsers.

How to Flush DNS on macOS

The process for flushing the DNS cache on macOS varies slightly depending on the version of the operating system. Each version uses a specific command to interact with its DNS resolver service.

Using Terminal for macOS

1. Open Terminal:
   • Navigate to Applications > Utilities > Terminal.
   • Alternatively, use Spotlight Search (Command + Space) and type “Terminal,” then press Enter.
2. Execute the Flush Command (Version-Specific):
   • macOS Monterey (12) and later:

     sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

   • macOS Big Sur (11) and Catalina (10.15):

     sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

   • macOS Mojave (10.14) and High Sierra (10.13):

     sudo killall -HUP mDNSResponder

   • macOS Sierra (10.12) and El Capitan (10.11):

     sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

   • After entering the command, you will be prompted to enter your administrator password. Type it and press Enter. The password will not be displayed as you type.

The sudo command grants administrative privileges for the operation, while dscacheutil -flushcache directly clears the DNS cache, and killall -HUP mDNSResponder restarts the mDNSResponder service, which manages DNS lookups.

Operating System	Command to Flush DNS
Windows	ipconfig /flushdns
macOS (recent)	sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
Linux (systemd-resolved)	sudo resolvectl flush-caches

How to Flush DNS on Linux

Linux distributions often use different DNS caching services, so the command to flush the cache can vary. Common services include systemd-resolved, dnsmasq, and nscd.

Using Terminal for Linux

1. Open Terminal:
   • Use the keyboard shortcut Ctrl + Alt + T.
   • Alternatively, find “Terminal” in your applications menu.
2. Identify and Execute the Flush Command (Service-Specific):
   • For systems using systemd-resolved (e.g., Ubuntu 17.04+, Fedora, Debian 9+):

     sudo resolvectl flush-caches

     To restart the service, which also clears its cache:

     sudo systemctl restart systemd-resolved

   • For systems using dnsmasq:

     sudo systemctl restart dnsmasq

     This command restarts the dnsmasq service, effectively clearing its cache.

   • For systems using nscd (Name Service Cache Daemon):

     sudo systemctl restart nscd

     Restarting the nscd service clears its cache.

   • No specific caching service: Many minimal Linux installations or older versions might not run a local DNS caching service. In such cases, there is no local cache to flush. The system directly queries external DNS servers for each request.

You will need to enter your administrator password when prompted by sudo. The specific command depends on which DNS caching service is active on your Linux distribution. Checking your system’s documentation or active services can help identify the correct method.

Verifying Your DNS Flush

After flushing your DNS cache, it’s beneficial to verify that the operation was successful and that your system is now resolving domain names correctly. While there isn’t always a direct “cache empty” confirmation, you can observe behavioral changes and use diagnostic tools.

• Re-test the Problematic Website: Attempt to access the website or service that was previously causing issues. If it now loads correctly or displays updated content, the flush was effective.
• Use ipconfig /displaydns (Windows): Immediately after flushing, running ipconfig /displaydns should show a significantly smaller or empty list of DNS entries, indicating the cache has been cleared. As you browse, entries will gradually reappear.
• Use dig or nslookup (Linux/macOS/Windows): These command-line tools can query DNS servers directly. After a flush, your first query for a specific domain should take slightly longer than subsequent queries for the same domain, as the initial lookup populates the cache.
  • Example: dig example.com or nslookup example.com
• Observe Network Activity: Tools like Wireshark or browser developer tools can show DNS query traffic. After a flush, you would expect to see new DNS queries for domains you visit for the first time in that session.

The primary goal is to ensure that your system is no longer relying on potentially stale or incorrect cached information and is instead obtaining fresh DNS records from the configured DNS servers.