2.2 Starting a Router  
  2.2.2 Router LED indicators  
Cisco routers use LED indicators to provide status information. Depending upon the Cisco router model, the LED indicators will vary.

An interface LED indicates the activity of the corresponding interface. If an LED is off when the interface is active and the interface is correctly connected, a problem may be indicated. If an interface is extremely busy, its LED will always be on. The green OK LED to the right of the AUX port will be on after the system initializes correctly.

 

Web Links

Reading the LEDs

http://www.cisco.com/en/US/products/ hw/routers/ps259/products_installation_ guide_chapter09186a008007e022.html#34028