This is a curious case where all the devices at hand will link with one another, except for two that just won't detect one another. One device is a single board computer (SBC) with a gigabit nic, the other is a fancy managed gigabit switch.
If I patch the computer into any other switch (have two others models on hand in the lab), computer and switch link up fine. If I plug other computers into the finicky switch, they link up fine, too. But this one SBC just won't even get a link light on any port with the finicky switch - it's as though the cable I plugged in just isn't even there. It's not only that the LED in the RJ45 doesn't light up - the 'port show' command in the switch's management console shows no hint of anything being connected. The ports are set to auto-detect.
I checked the cabling, of course. Cat5e, didn't ohm it, but looks like all four pairs are crimped into the RJ45s ok - besides, same cabling gets 1000Base links with other ports just fine.
At this point, I don't even care if the negotiated link is 10Base, I'd just like to see these ports light up as though they detect one another at all. What could cause something like this?