Problem Description: When you see network properties you may find red question mark on Ethernet connection with message “Authentication Failed”
This issue occurs because your Windows machine is either trying to use 802.1X authentication and network device on the other end (switch or DHCP Server) is not compatible with it or the network device is demanding 802.1X authentication but your machine is missing the required configurations.
Solution: You can stop “Wired AutoConfig” service on affected machine, change the startup type to manual and see if your machine gets an IP address. Please note sometimes a reboot is required for changes to be effective. Basically this solution is disabling an authentication at client end and it will only work if your network device is not demanding for 802.1X authentication. Some network switches will deny the connection even if you configure static IP to your machine.
Now, assume a case where you already applied the fix mentioned here and now see an exclamation mark on Ethernet connection with message “Unidentified Network”. Well, this is the situation where the switch/DHCP sever is asking for 802.1X authentication and your machine is not providing the credentials. First enable and start “Wired AutoConfig” service as the service is must for 802.1X auth. On the “Authentication” tab of Ethernet connection properties place a check mark next to “Enable IEEE 802.1X authentication”. If you still have trouble connecting to network then the credential supplied by your machine are rejected by network device. By default your Windows machine presents “Machine certificate” and in absence of valid certificate your machines credentials will be rejected by network device. Please install machines certificate from a CA trusted by your IP issuing network device and then your machine should connect to network. You can check if valid certificate is there on your machine by going to “Certificates” console (Start-> Run->MMC->Add/Remove Snap-in->Certificates-> Local Machine). In the certificate console, select Personal folder and see for the certificate with machine name.