My opinion is that there's differences between routers. Example: My friend who owns DSL with router (firewall/NAT/Router included) can't do game for some reason, and when I host a game in LFS demo (hopefully gonna be demo user 6 hours anymore) there's no proble at all, there is no lagg with 8 players racing no problems with connections or players (doen't mean starters=newbies).
So trep my suqqestion is that you should try first to open all gates from (in case your router does have one) firewall, and if that doesn't work then call your customer service and ask can you make servers or is it forbidden.
Of course you can allways try another router, that might help also.