by ailurophobe » 21 Sep 2011 14:45
If the port is closed it must be behind either a router or a firewall. Sometimes that is integrated to the modem, sometimes the router is run by the ISP (to conserve address space or do network management). In either case UPnP may or may not be supported. The important thing is that UPnP is much more likely to be supported than manual configuration by user. So worth a try.