Stealthing Ports with Netopia Dsl

Hey, I have tried everything I can think of to get all my ports in Stealth Mode. I have read in at least one place that Netopia will not allow stealthing. I am a Comodo Internet Security user. Anyone have a suggestion? I have tried all sorts of Network changes. I got 3 stealthed ports out of all. Anyone with knowledge on how this can be done, it will be greatly appreciated. ???