The Bombay Stock Exchange benchmark Sensex today opened higher by 80 points at 18,128. The sensex was trading at 18114, up by 65 points when reports last came in. Similarly, the broad-based National Stock Exchange index Nifty gained 21 points to trade at 5,435.Brokers said fresh on buying in realty and metal stocks by funds tracking firm global markets.Meanwhile, Hong Kong's Hang Seng index was up by 0.43 per cent, while the Japanese Nikkei gained 1.07 per cent in the morning trade today. The US Dow Jones Industrial average ended 1.01 per cent higher on Tuesday.