In general with XNET boards there are two LEDs per port. The first LED indicates whether the port is being used. The second LED gives information about the Bus. I have attached the NI XNET Hardware and Software manual. If you go to the LEDs section in section 3-17 there is a detailed description of what different LED behaviors mean.
NI-XNET Hardware and Software Manual
http://www.ni.com/pdf/manuals/372840h.pdf
Matt G.
Product Manager
National Instruments
