CNN reporter ducks for cover while reporting on the fighting in Ukraine

Just weeks after the crash of Malaysia Airlines Flight 17, Russia appears to be preparing for a major offensive in Ukraine. After a recent build-up of troops, there are now some 20,000 Russian forces gathered along the Ukrainian border. At the same time, Ukrainian forces are on the move and hoping to regain control of a key city. CNN's Nick Paton Walsh was forced to take cover from the fighting as he filed this report for AC360.