Nikon D6 Reference Manual page 652

A
The Viewfinder Display
Connection status is also shown in the
camera viewfinder. T is displayed when
the camera is connected via Ethernet, U
when it is connected to a wireless network.
The icon will flash if an error occurs.
A
Firewall Settings
TCP port 15740 and UDP port 5353 are used for connections to
computers. File transfer may be blocked if the server firewall is not
configured to allow access to these ports.
600
Camera Control