The Sensex at the Bombay Stock Exchange gained 126 points, or 0.7 per cent, to cross the 17,000 mark, at 17,084, on continued buying by investors, amid firm overseas markets, today.Later, after giving up all it early gains, on profit-booking, the Sensex once again rebounded, to stand 54 points, or 0.3 percent in positive territory, at 17,013 in volatile trade, a short while ago.Other Asian markets in Japan, China, Taiwan, Hong Kong, Indonesia, Singapore and South Korea were up by between 0.3 percent and 1.5 percent, today, on hopes that euro zone leaders will be able to hammer out a solution to the region's debt crisis.The US Dow Jones Industrial Average had closed 0.9 per cent higher, overnight.