The National Stock Exchange (NSE) has filed its Draft Red Herring Prospectus (DRHP) with market regulator SEBI for its IPO, which is likely to be the biggest in the country’s history. Some of the early backers of the exchange, classified as “selling shareholders”, are set for major gains as their acquisition costs are nearly negligible. Here’s a look at some of these names and how much they are likely to earn.