Is some foreign experience necessary to attain a professorship in India? I wish to know even the unwritten rules in this regard. Should one have at least a postdoc from abroad if one has done a PhD in India? I wish to include within the ambit of this question also those who have done either their graduation or post graduation from abroad.
In general, the best way to answer the question "What qualifications do I need for job X?" is to look up people who currently have job X and see what their qualifications are. So I suggest you go to the websites of several professors in India (ideally junior professors who were hired recently) and see what they did beforehand.