I'm new to Linux.
On Windows I'm used to have the firewall triggered automatically by an application and then I authorize whether or not to let the application access real world.
Linux using UFW has more manual approach which is OK by me.
What I found is an interesting phenomenon.
I opened port 51413 for Transmission on GUFW (Both TCP and UDP):
Yet still on Transmission it seems the port isn't open:
I thought maybe something isn't working with the UPNP (Though the same computer with Windows configure the Router with UPNP perfectly on Transmission for Windows). So I downloaded small utility to see the UPNP configuration - UPnP Router Control.
What I saw was very strange:
Skype configured ports using UPNP which means UPNP works.
Now the questions:
- It seems the UPNP is working, how come Transmission isn't able to properly open the port? Or even do it like Skype?
- How the hell Skype could bypass the UFW and open port to the outside world without any permission?
- What's the UPNP policy? Can any UPNP application just bypass the UFW?