The router acts as a firewall so that would explain it. Perhaps future versions will allow you to force the default port to whatever you wish.
For now you can set your router to allow incoming on port 6346 and map it ( forward it) to the computer you are using.
Although it will work with no configuration at all in your router ( depends on your set up) , by allowing that incoming port it will increase success rate.


If you need any help configuring your router, feel free to ask.
( if linksys log into admin panel > advanced options > forwarding )