AFAIK Motorola SB routers do not support UPnP. Which means you will need to forward a port within the device. Choose the port you wish to connect & listen through. You will need to check the manual for your Motorola about port forwarding. I do not have mac instructions. The windows one is here PortForward.com - Free Help Setting up Your Router or Firewall find model then click LW on next page.

The steps in forwarding a router are as follows with the first step the most important:

1. Setting up a static ip on Mac OSX (click on link)

2. Forward a port within the device. Save settings & reboot device. Reboot computer.

3. Settings within LW are Manual port forward instructions & sample image. However, the firewall tab is now found under the Advanced section. Choose same port number you used in port forward process.

4. If your OSX firewall is turned on then see OSX Firewall settings for Tiger