NL_Port (Node Loop Port):
A port on a node that connects to another port in an arbitrated loop
Private NL_Ports can only communicate with other loop ports
Public NL_Ports can communicate with other loop ports and with
N_Ports on an attached fabric
Note that the term L_Port (Loop Port) is sometimes used to refer to any port
on an arbitrated loop topology — either FL_Ports or NL_Ports.
If a node connects to a loop environment, we have a node loop port (NL_Port).
When a NL_Port is private there is no fabric loop port.
A private loop never has an FL_Port.
If there is a fabric loop port in existence then it forms a public loop.
A public loop always has an FL_Port.