The BSE Sensex rallied by over 220 points in opening trade today on fresh buying by funds and retail investors, driven by a firming trend in global markets.The 30-share index, which gained 17 points in yesterday's volatile session, surged by over 220 points, to around 17,702 in the first five minutes of trade today on the back of a rise in oil and gas, auto, metal, realty and IT sector stocks.In a similar fashion, the wide-based National Stock Exchange, Nifty, moved up by over 60 points, to around 5,326.