How do I find out why I2P thinks it's firewalled?

The device with I2P is behind a NAT router without UPnP. The device has a firewall but has opened the UDP and TCP port for internet facing communication. The ports from the router are forward to the device's ports. Are there any ports missing?

Edit: I finally figured it out. The port forwarding was only for TCP. It would be good to have logs or some kind of status window stating why it thinks it's firewalled though.