When you get against the ropes keep your regular stance and absorb the punches you will be able to counter with power if you keep your stance and don't pitter pat your punches while peaning all of your weight against the ropes...make sure you still push off your back foot for your power.

I had a problem with someone being overly aggressive to me in a sparring match, a good hook to the body will always slow them down. If you're bigger than him show him use your height or a weight advantage if you have it, back him up, shorter fighters don't fight as well going backwards it gives them less angles to attack.