The Transport node vmwNsxTDataCenterEntityId control plane connection to Manager node vmwNsxTDataCenterApplianceAddress is down for at least vmwNsxTDataCenterTimeoutInMinutes minutes from the Transport node's point of view. Action required: 1. Check the connectivity from Transport node vmwNsxTDataCenterEntityId to Manager node vmwNsxTDataCenterApplianceAddress interface via ping. If they are not pingable, check for flakiness in network connectivity. 2. Check to see if the TCP connections are established using the netstat output to see if the Controller service on the Manager node vmwNsxTDataCenterApplianceAddress is listening for connections on port 1235. If not, check firewall (or) iptables rules to see if port 1235 is blocking Transport node vmwNsxTDataCenterEntityId connection requests. Ensure that there are no host firewalls or network firewalls in the underlay are blocking the required IP ports between Manager nodes and Transport nodes. This is documented in our ports and protocols tool which is here: https://ports.vmware.com/. 3. It is possible that the Transport node vmwNsxTDataCenterEntityId may still be in maintenance mode. You can check whether the Transport node is in maintenance mode via the following API: GET https://<nsx-mgr>/api/v1/transport-nodes/<tn-uuid>. When maintenance mode is set, the Transport node will not be connected to the Controller service. This is usually the case when host upgrade is in progress. Wait for a few minutes and check connectivity again.