Port forwarding using Transmission & Mac Pro

Port forwarding is performed at your Router -- not at your Mac.

You instruct your Router that when requests come from the Internet for a particular port, they are to be forwarded to the same (or different) port on exactly THIS Mac [be sure you have a static local IP Address].

Inviting strangers from the Internet onto your work Mac is a significant security risk, and you should not do this step lightly. Some prefer to have a web site (on a service, somewhere else) that hosts their work instead, so that they do not have to compromise the security of their work Macs.

Unless you have exactly ONE computer at your location, you are using a Router to provide connections and dispense "strictly local" IP Addresses that are not reachable directly from the Internet. Your Router may also include the Switch function, which cross-connects your computers for File Sharing, using wired, wireless or mixed connections.

You connect directly to your Router (by entering its IP Address, (such as 192.168.0.1 or 10.10.0.1) into the top Bar in Safrai or your usual Browser. The Router responds with login information.

From there you need the Router manual for your specific model of Router.

Your Airpot extreme does not figure into this equation, because you are not using it to connect to the Internet through your Router -- you are using the Ethernet connection.

Port forwarding in this case will be accomplished by changing settings on your Comcast Business Gateway.

Examine the Comcast Business Gateway device for a sticker with the default admin name and password. It may be on the top or bottom.

Once you can log in as the device Admin, you will need the manual for that device's operation, (or Comcast online help) to change the settings in that device to do Port forwarding.

This article may provide some general background as to how this procedure would work:

http://www.wikihow.com/Set-Up-Port-Forwarding-on-a-Router

I run a Calendar Server on a specific Mac on my Network. I have manually forwarded port 8443 (encrypted access for calendar) forwarded to a specific Mac with a static IP Address on my local network. When Calendar requests come in, they will be presented to that port on that Mac, rather than standard Router firewall practice (discard unsolicited packets on port 8443).

There are also several port forwarding settings to accommodate other devices, that I did not specifically make. My Verizon Set-top-box (for TV watching) also appears on the Network, and it has added a port to the list, so that requests for port 35000 will be forwarded directly to its IP Address.

I do not know whether you need to explicitly add ports to Port forwarding, or whether your Mac software can do it automatically, but regardless, you will need to know what ports are to be forwarded, and you will need to verify that those ports are actually showing up in the list on your Router.

I also run a MineCraft Server. It requires a manual port forwarding of port 25565 to the Server computer's local IP Address. Then multiple Users with login privileges can connect and participate in Minecraft simulations.