External Networks belong to a single enterprise and they may have public or private IP addresses. VMs in more than one virtual datacenter can use IP addresses on the same external network. You can make an external network the default for an enterprise's datacenters or virtual datacenters, thus streamlining the configuration of access to networks outside the virtual datacenter.
In private cloud, an administrator defines the external network in the network infrastructure (VLANs in the switch or network manager), and then a cloud administrator creates the corresponding network in the platform, supplying the VLAN tag or VXLAN tag. In vCloud Director, an administrator may onboard and synchronize external networks, but they may not manage them in the platform.