On my Dell U3224KBA I noticed that tagged VLAN ethernet behaved strangely, some destinations I could reach, others partially. The strangest was I could SSH into my router, run ‘small’ commands, but the connection would freeze when I ran a command with more text output.

Realtek firmare - didn’t help ¶

Dell has an article on this called “Realtek USB GBE Ethernet Controller Driver Fails to Get Valid IP Address When Using VLAN IDs Set for the Adapter” (dell.com), which is not the same but close, and made me realize the Dell monitor ethernet controller has firmware I can update.

Instructions how to get firmware are here (dell.com), the ones for my display are listed here (dell.com). There is a ‘critical’ Realtek USB GBE Ethernet Controller Driver, which can only be updated on Windows. Running this seems to fix/not fix the issue.

Display firmware - didn’t help ¶

Additionally, I updated my firmware from M2T104 to M2T107.

Interface MTU - helped ¶

I found that SSH got stuck at debug1: expecting SSH2_MSG_KEX_ECDH_REPLY, which is also mentioned here (serverfault.com) and here (askubuntu.com), pointing to incorrect MTU. While these articles concern VPN, in my case VLAN similarly adds MTU overhead and could cause problems.

Setting the MTU manually to 1496 (subtracting 4 bytes for VLAN overhead) solved the issue. However it’s not clear why another adapter does not have the same problem. Also, the MTU is reset after re-pluggin the device, so it’s not a permanent fix.