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Clearing DNS Cache and Changing DNS server settings

dns-smallWhen a domain name‘s nameservers change, there can be an annoyingly long wait until those DNS changes propagate and the website becomes accessible again.

Apart from waiting for your ISP having to refresh the DNS cache on their servers, there are a few other things you can do on your local PC to accelerate DNS propagation.

Sometimes a reboot is sufficient, but there are quicker ways of solving the problem.

Clearing DNS Cache in Windows

The first method to try is the command line utility ipconfig, this allows you to force Windows to clear its local DNS Cache.

The DNS cache holds a record of all the websites you have visited and their IPs, so the next time you request a website, Windows looks in its DNS cache. The cache is deleted every 24 hours. However, if a website’s DNS information has changed more recently than that, or the cache has stored a negative response (due to a high level of network congestion or server load) the cache becomes outdated and can lead to browsing problems.

Follow this simple procedure to clear your DNS cache:

    1. Go to Start, Run and enter “cmd”
    2. Type “ipconfig /flushdns” into the command prompt.
    3. Press Enter. You will be informed that your DNS cache has been cleared.
    4. If you experience problems refreshing the cache you could also try the following commands in the stated order(press enter after each command)

 

ipconfig /release
ipconfig /renew
ipconfig /flushdns

Clearing DNS cache in Apple OS X

OS X Mountain Lion or Lion

Use the following Terminal command to reset the DNS cache:

sudo killall -HUP mDNSResponder

Mac OS X v10.6

Use the following Terminal command to reset the DNS cache:

sudo dscacheutil -flushcache

Clearing DNS cache in Linux

To Flush the DNS cache in Linux, you will need to restart the nscd daemon by entering the following into terminal:

sudo /etc/rc.d/init.d/nscd restart

Or

sudo /etc/init.d/nscd restart

Or

sudo /etc/init.d/dnsmasq restart

Or

/etc/init.d/named restart

 

Using Google’s plublic DNS servers

If clearing DNS cache did not fix the issue you can also try using Google DNS as your DNS provider. Google DNS generally refreshes more regularly than most ISPs, propagating any DNS changes more rapidly.

Before you change your DNS settings to use Google Public DNS, be sure to write down the current server addresses or settings on a piece of paper. It is very important that you keep these numbers for backup purposes, in case you need to revert to them at any time.

Please note that Google recommends that only users who are proficient with configuring operating system settings make these changes.

The Google Public DNS IP addresses (IPv4) are as follows:

  • 8.8.8.8
  • 8.8.4.4

The Google Public DNS IPv6 addresses are as follows:

  • 2001:4860:4860::8888
  • 2001:4860:4860::8844

Because the instructions differ between different versions/releases of each operating system, we only give one version as an example. If you need specific instructions for your operating system/version, please consult your vendor’s documentation.

Microsoft Windows

DNS settings are specified in the TCP/IP Properties window for the selected network connection.

Example: Changing DNS server settings on Microsoft Windows 7

  1. Go the Control Panel.
  2. Click Network and Internet, then Network and Sharing Center, and click Change adapter settings.
  3. Select the connection for which you want to configure Google Public DNS. For example:
    • To change the settings for an Ethernet connection, right-click Local Area Connection, and
      click Properties.
    • To change the settings for a wireless connection, right-click Wireless Network Connection, and click Properties.

    If you are prompted for an administrator password or confirmation, type the password or provide confirmation.

  4. Select the Networking tab. Under This connection uses the following items, select Internet Protocol Version 4 (TCP/IPv4) or Internet Protocol Version 6 (TCP/IPv6) and then click Properties.
  5. Click Advanced and select the DNS tab. If there are any DNS server IP addresses listed there, write them down for future reference, and remove them from this window.
  6. Click OK.
  7. Select Use the following DNS server addresses. If there are any IP addresses listed in the Preferred DNS server or Alternate DNS server, write them down for future reference.
  8. Replace those addresses with the IP addresses of the Google DNS servers:
    • For IPv4: 8.8.8.8 and/or 8.8.4.4.
    • For IPv6: 2001:4860:4860::8888 and/or 2001:4860:4860::8844
  9. Restart the connection you selected in step 3.
  10. Confirm that your setup is working correctly.
  11. Repeat the procedure for additional network connections you want to change.

Mac OS X

DNS settings are specified in the Network window.

Example: Changing DNS server settings on Mac OS 10.5

  1. From the Apple menu, click System Preferences, then click Network.
  2. If the lock icon in the lower left-hand corner of the window is locked, click the icon to make changes, and when prompted to authenticate, enter your password.
  3. Select the connection for which you want to configure Google Public DNS. For example:
    • To change the settings for an Ethernet connection, select Built-In Ethernet, and click Advanced.
    • To change the settings for a wireless connection, select Airport, and click Advanced.
  4. Select the DNS tab.
  5. Click + to replace any listed addresses with, or add, the Google IP addresses at the top of the list:
    • For IPv4: 8.8.8.8 and/or 8.8.4.4.
    • For IPv6: 2001:4860:4860::8888 and/or 2001:4860:4860::8844
  6. Click Apply and OK.
  7. Confirm that your setup is working correctly.
  8. Repeat the procedure for additional network connections you
    want to change.

Linux

In most modern Linux distributions, DNS settings are
configured through Network Manager.

Example: Changing DNS server settings on Ubuntu

  1. In the System menu, click Preferences, then click Network Connections.
  2. Select the connection for which you want to configure Google Public DNS. For example:
    • To change the settings for an Ethernet connection, select the Wired tab, then select your network interface in the list. It is usually called eth0.
    • To change the settings for a wireless connection, select the Wireless tab, then select the appropriate wireless network.
  3. Click Edit, and in the window that appears, select the IPv4 Settings or IPv6 Settings tab.
  4. If the selected method is Automatic (DHCP), open the dropdown and select Automatic (DHCP) addresses only instead. If the method is set to something else, do not change it.
  5. In the DNS serversfield, enter the Google Public DNS IP addresses, separated by a space:
    • For IPv4: 8.8.8.8 and/or 8.8.4.4.
    • For IPv6: 2001:4860:4860::8888 and/or 2001:4860:4860::8844
  6. Click Apply to save the change. If you are prompted for a password or confirmation, type the password or provide confirmation.
  7. Confirm that your setup is working correctly.
  8. Repeat the procedure for additional network connections you want to change.

If your distribution doesn’t use Network Manager, your DNS settings are specified in /etc/resolv.conf.

Example: Changing DNS server settings on a Debian server

  1. Edit /etc/resolv.conf:
    sudo vi /etc/resolv.conf
  2. If any nameserver lines appear, write down the IP addresses for future reference.
  3. Replace the nameserverlines with, or add, the following lines:For IPv4:
    nameserver 8.8.8.8
    nameserver 8.8.4.4

    For IPv6:

    nameserver 2001:4860:4860::8888
    nameserver 2001:4860:4860::8844
  4. Save and exit.
  5. Restart any Internet clients you are using.
  6. Confirm that your setup is working correctly.

Additionally, if you are using DHCP client software that overwrites the settings in /etc/resolv.conf, you will need to set up the client accordingly by editing the client’s configuration file.

Example: Configuring DHCP client sofware on a Debian server

  1. Back up /etc/resolv.conf:
    sudo cp /etc/resolv.conf /etc/resolv.conf.auto
  2. Edit /etc/dhcp3/dhclient.conf:
    sudo vi /etc/dhcp3/dhclient.conf
  3. If there is a line containing domain-name-servers, write down the IP addresses for future reference.
  4. Replace that line with, or add, the following line:For IPv4:
    prepend domain-name-servers 8.8.8.8, 8.8.4.4;

    For IPv6:

    prepend domain-name-servers 2001:4860:4860::8888, 2001:4860:4860::8844;
  5. Save and exit.
  6. Restart any Internet clients you are using.
  7. Test that your setup is working correctly.

Routers

Every router uses a different user interface for configuring DNS server settings; we provide only a generic procedure below. For more information, please consult your router documentation.

Note: Some ISPs hard-code their DNS servers into the equipment they provide; if you are using such a device, you will not be able to configure it to use Google Public DNS. Instead, you can configure each of the computers connected to the router, as described above.

To change your settings on a router:

  1. In your browser, enter the IP address to access the router’s administration console.
  2. When prompted, enter the password to access network settings.
  3. Find the screen in which DNS server settings are specified.
  4. If there are IP addresses specified in the fields for the primary and seconday DNS servers, write them down for future reference.
  5. Replace those addresses with the Google IP addresses:
    • For IPv4: 8.8.8.8 and/or 8.8.4.4.
    • For IPv6: 2001:4860:4860::8888 and/or 2001:4860:4860::8844
  6. Save and exit.
  7. Restart your browser.
  8. Confirm that your setup is working correctly.

Information cited from Google