Ike's jab is basically his whole game. It's good. Like, cancel into itself for nearly 20% good. And it's fast. And it has crazy reach. So here's the deal:
If he starts jabbing you just di away. Don't bother trying to go through it, it's not worth it. Never run in there when he has a full shield. Wear him down with fireballs. You'll either force him to approach (where you can win with superior speed), or you'll reduce his shield enough that you can get in there with a crossover dair to start things. Just be careful, and make him play at your pace...his fsmash can change the game in a second if you start rolling thoughtlessly.