An alarm reports a loss of uplink redundancy on a vSphere standard or a distributed switch for a host.
No redundant physical NICs for a host are connected to a particular standard or a distributed switch, and the following alarm appears:
Host name or IP Network uplink redundancy lost
Only one physical NIC on the host is connected to a certain standard or a distributed switch. The redundant physical NICs are either down or are not assigned to the switch.
For example, assume that a host in your environment has physical NICs vmnic0 and vmnic1 connected to vSwitch0, and the physical NIC vmnic1 goes offline, leaving only vmnic0 connected to vSwitch0. As a result, the uplink redundancy for vSwitch0 is lost on the host.
Check which switch has lost uplink redundancy on the host. Connect at least one more physical NIC on the host to this switch and reset the alarm to green. You can use the vSphere Web Client or the ESXi Shell.
If a physical NIC is down, try to bring it back up by using the ESXi Shell on the host.
For information about using the networking commands in the ESXi Shell, see vSphere Command-Line Interface Reference. For information about configuring networking on a host in the vSphere Web Client, see vSphere Networking.