I complained that day itself and didn’t get any response. Next day I rushed to BSNL office and asked the person who is in charge of the broadband. He said he has to check the modem. I gave the modem and he changed something. He said it will work. I asked what was the problem. He said the connection settings were updated and gave me a print out with new connection settings.

The brief of printout:

We are happy to announce the commissioning of the Broadband Multi Play equipment in your exchange area. Consequently your Broadband connection is being upgraded and the service will be provided from the new Multi Play network. New services like IPTV, Video on demand etc are going to be introduced in near future.

And it is said that the existing userids and passwords will be change.
Is it their duty to inform the client about new changes? We can say it as lack of professionalism.

Before you configure new DNS, It is adviced that be sure to write down the current   settings on a piece of paper. One thing I noticed that unlike the Open DNS it is very easy to remember.Google has given a detailed configuration settings here.

How to configure Google Public DNS on your Ubuntu?

The Google Public DNS IP addresses are as follows:
8.8.8.8
8.8.4.4

It is very easy to configure these DNS IP addresses on your Ubuntu.

Steps
1. Right-click on ‘Network Icon’ (located at top-right panel by default) and click on ‘Edit Connections’ to open Network Connections Manager.
2. Choose the type of connection you have. For this example, I will use ‘DSL’.
3. Under ‘DSL’, highlight ‘BSNL BB’ (my broadband connection) and click on ‘Edit’.
4. Inside ‘Editing BSNL BB’ window, click on ‘IPv4 Settings’ tab.
5. Under ‘IPv4 Settings’, change the ‘Method’ to Automatic (PPPoE) addresses only.
6. Put these nameserver addresses as your ‘DNS Servers’: 8.8.8.8, 8.8.4.4
7. Click ‘Apply’ and reboot your machine. You are done. Now your DNS has pointing to Google Public DNS.