Sometimes I find that there is browser error accessing websites. Never the less when I enter numeric IP address (like 72.14.221.104 for google.com) there is no error and web page loads normal. This indicates that BSNL's DNS server is not working.

If you want to manually enter DNS server addresses just for tweaking or experimenting, these may be any one of the following:
218.248.255.145
61.1.96.71
61.1.96.69
61.1.96.65
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