Do you really need to forward ports to play on System Link?

i made a thread on RMS and the expert said its not needed to forward ports when youre only gonna play and not create a room: http://www.realmodscene.com/index.p...r-system-link-over-carrier-grade-nat/?p=49469

By the way, the reason why i dont forward ports is because my ISP disallowed it over carrier grade NAT.
People are recommending to use a VPN but i think its not possible since xbox is not capable of VPN..

What do you guys think?