To check NIC link status from the ESXi service console

Run this command:

esxcli network nic list

The output should come up similar to:

Name     PCI Device    Driver  Admin Status  Link Status   Speed  Duplex  MAC Address         MTU  Description
-------  ------------  ------  ------------  -----------  ------  ------  -----------------  ----  -----------
vmnic0   0000:01:00.0  ixgben  Up            Up             1000  Full    ec:f4:bb:da:b6:c8  1500  Intel(R) Ethernet Controller X540-AT2
vmnic1   0000:01:00.1  ixgben  Up            Up             1000  Full    ec:f4:bb:da:b6:ca  1500  Intel(R) Ethernet Controller X540-AT2

Note: The Admin Status is the only portion of the output that ESXi controls. The link status column specifies the status of the link between the physical network adapter and the physical switch. The link status can be either Up or Down.

To change the Admin status of the physical interface from the command line interface

Note: Only cards running auto-negotiation/10Mb/100Mb/1000Mb/10000Mb speeds are supported.

1. Log in to the ESXi host using Tech Support Mode with root account privilege.
2. Change the admin status of the uplink vmnic by running one of these commands:
   
   esxcli network nic down -n vmnicX
   esxcli network nic up -n vmnicX
   
   Where X is the vmnic number (for example,vmnic0)
   
   Important: If the Link Status shows the link as down, contact the host hardware vendor for troubleshooting. For more information, see Network adapter (vmnic) is down or fails with a failed criteria code (2014553).