USB-C Hubs and Ethernet (2020)

This has happened with other ethernet controllers too. It&#x27;s about the fact that they can send pause frames when the host disconnects while the power is still on.<p>You can also do this with USB-A, get an USB-A controller that sends pause frames, plug it into a powered USB hub and connect to your computer. Unplug, watch the ethernet link still being online and suddenly the network dies. Mostly happens with Realtek USB Ethernet controllers.<p>This is a firmware feature so technically you can turn it off.<p>If you want to try it with PCI or PCIe: get a powered backplane or bifurcation board or thunderbolt-to-pci bridge. Connect&#x2F;use as normal then disconnect the host while leaving power on. Same problem happens with controllers that send pause frames.

Author here: so since I wrote this blog post I get an email once every few weeks about this. Apparently that blog post ranks quite well now for the keywords that frustrated users are typing into Google.<p>I have now heard that this problem happens with a lot of devices and the most common element in most of them is that people also have netgear switches on their network but not exclusively.<p>The most reliable workaround is to ensure that the USB-C adapter with an ethernet card in it is powered off when the laptop goes to sleep. Many do that if they are not also used for USB-C PD or whatever it&#x27;s called.

&gt; <i>nodes sending PAUSE message to the special multicast address 01:80:C2:00:00:01 are instructing the switch to not send them any more frames. My switch seems to honor this, but also forwards the frames to the other nodes on the network, in effect telling THEM to pause in sending frames, which would explain the observed behavior.</i><p>The what now? I&#x27;ve never heard of &quot;PAUSE&quot; frames before, but those sound like a feature just waiting to be exploited.<p>Do we know how common the behaviour to forward the frames is? This sounds like it could bring down any vulnerable public network of their choice by just logging on and sending that special packet...

I just went through exactly this. I’d unplug my laptop, walk downstairs and suddenly the WiFi would stop working.<p>To troubleshoot, I’d plug into the hub to have Ethernet connectivity, and the network would seem to work fine. Took me weeks of guessing before considering that a powered-but-disconnected USB hub could be the culprit.<p>Odd that this is an issue across so many vendors. Perhaps they share a chip, but still, it reads as a mistake on the Hub as well as the Switch side of things.

I have USB 3.0 and 3.1 hubs; I am not surprised about this article. USB 3.0&#x2F;3.1 hubs are fickle as heck! And I noticed that they seem to emit some kind of EMF around the port which means they are unshielded. It rendered some USB dongle non-functional until I unplug the hub.<p>Now I have Anker 3.1 Mini-Dock (without the ethernet), it works well but it has issues with HDMI. For whatever the reason, the system think that the HDMI is plugged in the hub whereas it is not. So, It cause a strange issue with multimonitor since the system believes that there is a second monitor plugged to it. But yet it couldn’t show the second monitor in the display setting but it insists that it is plugged.

I use a USB-C&#x2F;Thunderbolt dock from CalDigit that seemingly has the same problem. Luckily they released a firmware update that supposedly fixes it several months back.<p>I&#x27;m guessing a lot of the manufacturers just ended up using the same chip for their docks&#x2F;hubs, and some manufacturers just don&#x27;t care if there was a firmware update from the chip vendor.

A year ago spend relatively long time troubleshooting my home network problem and the root cause was the same: 1. USB-C hub with an Ethernet port send pause frames when it is powered but a laptop is disconnected 2. TP-Link Wi-Fi router broadcasts pause frames to all ports which causes all connected devices to stop sending traffic.<p>TP-Link (or more specifically Atheros AR8327 used inside it) here is likely breaks a IEEE standard (may be even the most basic one - 801.2d), but when no-one send pause frames this goes unnoticed.<p>As workaround now don&#x27;t connect power to the hub and instead connect charger to a laptop directly (if a hub is powered you can connect only one cable to s laptop to get both - power and external USB+Ethernet).

USB-C hubs that I’ve used have been garbage. They’ve all crapped out after less than a year or so of use. The Dell USB-C docking stations I’ve had have been flawless. Not sure what the diff is as my Dell puck USB-C hub sucked (went through 2 of them in a year), but the docking stations are solid.<p>The one difference I see is that the docking stations are meant to be independently powered and I think it has its own fan. I’m sure the internals are different too, but I don’t know how. Curious if anyone knows more about the difference between the hardware&#x2F;firmware on the hubs vs the stations.

Why do these hubs (or the chips they&#x27;re made with) want to send PAUSE frames in the first place? What&#x27;s the potential advantage vs just behaving as a switch with no other devices connected?

I&#x27;ve had good luck with a Thunderbolt 4 Hub from Anker as of late. The hub has a power button of its own, and when the hub is turned off it turns off the attached USB-C-to-Ethernet adapter.

Note that this doesn&#x27;t seem to actually be related to USB-C, but rather to a quirk of how the docking station the author was using behaved when not connected to a computer. This could just as easily happen with any dock. But maybe USB-C and Apple&#x27;s dongle life has made such docks more common.

over under on when USB-C will finally &quot;just work&quot;?<p>five years ago I would have said five years<p>now I&#x27;d say 10

tl;dr: cheap hubs with ethernet failed, dedicated Apple ethernet adapter worked. Author still isn&#x27;t sure exactly why.