Useful when you lost access if you forcibly set speed duplex for vmnic instead of recommended by ESXi which doesn’t support manually set speed duplex because of bad RJ-45 cable type or switch.

• Open ESXi console, press F2 and enter root credentials
• Open Troubleshooting Options > Enable ESXi Shell
• Press ALT+F1 to enter ESXi Shell
• Enter root credentials and list all vmnic and enable Autonegotiating byt switch -a, after set vmnic UP

esxcli network nic list
esxcli network nic set -n vmnic0 -a
esxcli network nic up -n vmnic0

• To enter back ESXi console press ALT+F2
• TIP: you can look into vmkernel.log and search for Uplink keyword when you have some problem with vmnic.