Hmmm? Explain please?
For some, if not most routers, you have to set up a static IP for the ports to be forwarded to. This involves setting the ports on your router's port forwarding page to be forwarded to a specific IP and setting up your hosting computer to have a static IP.
Without setting up a static IP, basically your router is going, "Oh God, wtf, I have these users who want to connect to this forwarded port, but I don't know which computer in this network to send them to oh God what the forget".