In recent days,I think bsnl has blocked websites like github,vimeo and many other useful sites. Do not worry guys,you can still access those sites which are blocked by your ISP by doing little configuration in your computer.you can use "Google DNS" to unblock the websites which are blocked by your ISP. Google provides it's own DNS to access websites which is free.

Follow this steps to use Google DNS :

Microsoft Windows:
[IPV4]

[IPV6]
DNS settings are specified in the TCP/IP Properties window for the selected network connection. 
Example: Changing DNS server settings on Microsoft Windows 7/8
  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) orInternet 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. 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.

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 servers field, 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.
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 nameserver lines 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.
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.

Mobile or other devices

DNS servers are typically specified under advanced wi-fi settings. However, as every mobile device uses a different user interface for configuring DNS server settings, we provide only a generic procedure below. For more information, please consult your mobile provider's documentation.
To change your settings on a mobile device:
  1. Go to the screen in which wi-fi settings are specified.
  2. Find the screen in which DNS server settings are specified.
  3. If there are IP addresses specified in the fields for the primary and seconday DNS servers, write them down for future reference.
  4. 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
  5. Save and exit.

Testing your new settings

To test that the Google DNS resolver is working:
  1. From your browser, type in a hostname (such as http://www.google.com/). If it resolves correctly, bookmark the page, and try accessing the page from the bookmark. If both of these tests work, everything is working correctly. If not, go to step 2.
  2. From your browser, type in a fixed IP address. You can use http://18.62.0.96/ (which points to the websitehttp://www.eecs.mit.edu/) as the URL.* If this works correctly, bookmark the page, and try accessing the page from the bookmark. If these tests work (but step 1 fails), then there is a problem with your DNS configuration; check the steps above to make sure you have configured everything correctly. If these tests do not work, go to step 3.
  3. Roll back the DNS changes you made and run the tests again. If the tests still do not work, then there is a problem with your network settings; contact your ISP or network administrator for assistance.

Switching back to your old DNS settings

If you had not previously configured any customized DNS servers, to switch back to your old settings, in the window in which you specified the Google IP addresses, select the option to enable obtaining DNS server addresses automatically, and/or delete the Google IP addresses. This will revert your settings to using your ISP's default servers.
If you need to manually specify any addresses, use the procedures above to specify the old IP addresses.
If necessary, restart your system.



Note: The new connection will work when next time you connect,so it would be good choice if you just restart your computer and connect again. Google dns not only unblock those sites but it will also increase your internet speed.

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