Comment 1 for bug 621343

Hi! Thanks for filing this bug and helping to make Ubuntu better!

This is expected behaviour, as shutting down the NIC in some cases will cause Wake on Lan to be unusable later (e.g. at some point Windows' broadcom drivers would shut down a port making it totally unusable in Ubuntu). Additionally, this does not appear to be an issue with NetworkManager since other systems (e.g. ifupdown) also touch the interface, and ultimately the kernel will be what is dealing with the NIC.

As you were able to link from Apple support forums: http://lists.apple.com/archives/macos-x-server/2004/Nov/msg00199.html:
"We've almost always traced this down to a termination issue. Packets transmitted (unicast) aren't getting echo'd back to the NI properly. When you transmit a packet you're supposed to be able to hear it echo back. This can be caused by excessive traffic, dropped packets, collisions, or a switch that can't forward. It's also a function of the NI being able to handle the traffic. But it's basically a frame problem.

You can confirm this with a sniffer. Just don't run the sniffer on the same host as it's already loosing packets."

This is likely caused by the switch not doing its job right. My understanding is even if the interface stays up (and I have used systems other than Apple/OSX on a network with Ubuntu machines offline successfully), the switch should be able to mark the link at the spanning tree level as being down, the only thing being sent to the offline device being BPDUs (and nothing coming from it).

This really looks to me like an OSX bug or a hardware defect and not an issue with NetworkManager or even Ubuntu.

My suggestion is to follow the advice in the apple forum linked above, and run a sniffer on a third system (probably better if it is not an OSX device or the shutdown Ubuntu machine :), and see if there is traffic from the MAC address of the device that should be offline that reaches the other systems (as it would be broadcasted, otherwise the system isn't really offline). Another possibility would be to bring up the bug at Apple (through support or whatever facilities they have), since their systems need to be able to deal properly with "interference", or unsollicited packets.

For now, I'm marking this bug as Invalid. If you can provide a packet capture that shows there is indeed traffic coming from the offline Ubuntu system (and that this can provably be linked to not shutting down the NIC, which would still much more likely mean it's a bug in NIC firmware), then don't hesitate to re-open this bug or file a new one that refers to this bug number and case.

Thanks again!