The port that vCenter Server uses to listen for data transfer from its clients is 443. If you have a firewall between vCenter Server and its clients, you must configure a connection through which vCenter Server can receive data from the clients.
To enable vCenter Server to receive data from the vSphere Web Client, open port 443 in the firewall to allow data transfer from the vSphere Web Client to vCenter Server. Contact the firewall system administrator for additional information on configuring ports in a firewall.
If you are using the vSphere Web Client and do not want to use port 443 as the port for vSphere Web Client-to-vCenter Server communication, you can switch to another port by changing the vCenter Server settings in the vSphere Web Client. To learn how to change these settings, see the vCenter Server and Host Management documentation.