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Old 11-27-2017, 09:39 PM   #1
abbiecd
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Join Date: Nov 2017
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Question Ubuntu with DL-6xxx (VisionTek Dual) no ethernet bridging?

I am seeking direction on where to figure out an issue with my new VisionTek DL dock. The dual + 4K support seems to work fine with Ubuntu (not so hot with Fedora, worked across first reboot and failed with crtc after that), and now that's been stabilized I'm trying to breathe life back in to my VM's.

I'm migrating from a Lenovo x230t to a Dell Precision m3520 and the onboard Lenovo E1000 always "swapped wires" when docked but the NIC never actually disappeared when undocked. The E1000 in the Lenovo and the E1000E in the m3520 both work fine, but the net-usb on the DL using the cdc-ncm module doesn't appear to support Linux bridging at all.

If I associate my VM's with a bridge (virsh net-edit) having slaves of usb0 (DL/cdc-ncm) and eth0 (onboard/e1000e) I can change the cabled uplink between the two respective ethernet jacks, where the other end plugs in to another laptop with IP and auto MDI-X, and observe that a continuous ping works properly out from the VM, through the bridge with the onboard E1000E of the Precision but not on the DL ethernet port. When the slave usb0 is live, I can see the arps, but the arps never make it back to the bridge. When the slave eth0 is live, the arps make it, and ping continues business as usual.

When I create VLAN subinterfaces usb0.612 and eth0.612 on the Precision without using any bridge, and also complete similar setup on the other laptop with a subinterface of enp2s0.612, clear IP's and reset IP's appropriately, and stick to just between Linux to Linux with no VM's involved, it works fine.

This indicates to me that the DL/cdc-ncm does support VLANs (802.1q) just not bridging. I don't know if usb-net is affected, or whether this is as granular as manufacturers who leverage cdc-ncm -- I simply don't know where else to look and I've already burned the better part of a day on this issue.

My whole point of having this dock is so I don't have to unplug any more than a dock cable and the power cable. Without support for bridging on the DL dock, I must also use the Precision's onboard E1000E.

Any pointers/tips on where to continue my search as to why the usb-net cdc-ncm in the DL isn't bridging?

Last edited by abbiecd; 11-27-2017 at 09:46 PM.
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