Is it possible for my modem to have a firewall?

I've exhausted all other possibilities. If this does not help, I will just have to accept that I cannot forward my ports at my dad's house. Let's assume for a second that I know how to forward ports. When I take my PC to my mom's house (exact same router, PC), I'm perfectly connectable. the only thing that changes is the ISP, and in turn, the modem. Here at my dad's we have Qwest DSL, while my mom uses Roadrunner.

So, is it possible that something in the modem, or the ISP itself, is acting as a firewall? And if so, how would I get around that?

Thanks a lot to anyone who has any ideas. I really do appreciate it.

whats your modem name and version

It's definitely possible that the isp could be blocking ports....

Some crappy providers over here block ports.

Best ring up your isp and ask them or some guy's here might know :)

Good luck

sand......vine