[Cialug] Meaning of ethernet connectivity light

[Andrew Vick]

I've been on the phone with Qwest tech support because I can't connect my home computer to the internet; it seems that my computer cannot communicate with the Actiontec modem.  The modem is connected via an ethernet cable, and the little ethernet light shows green, but tech support is suggesting that the ethernet card is bad.

Does anyone know how much needs to be working with the card/cable/modem in order to get the ethernet connection light to go on, or how much can be wrong before it goes off?  I'm curious about the general case as much as anything specific to my setup.  How much functionality does that light indicate?

-Andrew V.