Wed Jul 12, 2017 12:51 pm
the green LED means that the physical interfaces can each 'see' down the cable to the other end, and can signal each other as necessary to communicate at the set line speed.
To carry the metaphor further, if the physical interface on the switch's side gets a poke in the eye from a static spike or something, sometimes it will 'squint', rather than keeping it's eye all the way open- this will leave it unable to 'see' the entire way down the cable.. The physical interfaces will attempt to negotiate a lower line speed, and if unable to, you won't get a link on that port.
You should have no trouble getting a link at even 100m, with a properly functioning system - my assumption, here, backed by what you're telling me, is that something isn't working correctly. This is why the question about cable diagnostics with nothing plugged in - which you missed answering :)
