Problems with 802.1x authentication and DisplayLink docks
802.1x authentication is fully supported by DisplayLink docks, however it may require some further configuration of the Ethernet on the dock or the authentication to get it to work as expected.
If 802.1x is not working, please check the following common reasons for failure below
Check the version of DisplayLink software in use
The behaviour of the Ethernet driver with VLAN configuration was updated in v7.7 M4 to change the way VLANs were applied to the Ethernet connection from an 802.1x authentication.
Previously VLANs were disabled and the VLAN ID was set to be 0. If VLANs were enabled the packets would have been priority tagged (VLAN set to zero). This was quite legal, but different behaviour to other Ethernet adapters.
The common behaviour is to have Priority and VLAN enabled, and the VLAN field set to zero, but still sent untagged traffic. When we changed our driver to have the same behaviour in 7.7 M4, it fixed these problems with 802.1x failures, as they could probably now enable VLANs and set the VLAN field in the same way is they did on other adapters.
MAC based authentication
If the 802.1x uses MAC address based authentication, this authentication will fail with a DisplayLink dock, as the MAC address is now the MAC address of the dock, not the MAC address of the laptop or tablet. To fix this issue, add the MAC addresses of the docking stations to the whitelist of allowed devices.
Check the MTU of the Ethernet interfaces
Some applications change the MTU of the laptop Ethernet interface, for example the Cisco VPN client. If the MTU is different on the DisplayLink adapter, the packets might be too large for the network infrastructure and truncated when sent over some links.
The Ethernet interface MTU settings can be checked with the windows command:
netsh interface ipv4 show subinterfaces
This shows an output similar to the one shown below
MTU MediaSenseState Bytes In Bytes Out Interface
------ --------------- --------- --------- -------------
1500 2 2357246 829669 WiFi
1500 5 0 0 Ethernet 4
1500 1 29038224 12937531 Ethernet 12If the MTU of the DisplayLink interface differs, the MTU can be changed to match the other interfaces. Eg:
netsh interface ipv4 set subinterface "Ethernet 4" mtu=1300 store=persistent
More information on setting the MTU can be found in this article.