Facebook is not opening from today morning, looks like it is blocked in India. It is not clear why they blocked, may be because of the ongoing legal battle with the Government over censoring objectionable content or related to some other legal issue.
Facebook website is throwing DNS error when I tried to open now. Till yesterday it was ok, so the block might have started from today. I am using TIKONA broadband, I have sent a mail to them asking about the reason for the block. I tried to access it through a proxy it is opening. So it is related to only India. Airtel is also blocking Facebook, I have a Airtel data connection, I tried to open in my mobile, but it is throwing error.
Facebook iOS app is working fine, there is no block for the app though.
I will update the post with details comments from the ISPs.
I spoke to a Tikona customer care executive. She said there is an issue with Facebook and will be online in two hours.
Meanwhile you can change your DNS to Google Publick DNS addresses. Use 18.104.22.168 and 22.214.171.124 addresses to change to Google DNS servers
Facebook is up again.