A vCloud Director external network provides an uplink interface that connects networks and VMs in the system to a network outside of the system, such as a VPN, a corporate intranet, or the public Internet. An external network must be created by the system administrator, and can be backed by one or more vSphere networks.
If you have more than one vCenter server registered to the system, you can create multiple external networks, each backed by a vSphere network. You can also create external networks that are backed by multiple vSphere networks, one from each of your vCenter servers. This approach can simplify IP address management in vCloud Director. You can modify the properties of an external network to change its network backings.
External Networks Backed by A Single vSphere Network
When an external network is backed by a single vSphere network, the system administrator must manage allocation of IP addresses used by consumers of the external network in all organizations. This requires manually configuring IP ranges on the underlying VLAN to provide each consumer of the external network with a non-overlapping set of IP addresses on the vSphere network.
External Networks Backed by Multiple vSphere Networks
An external network can be backed by multiple vSphere networks, subject to several constraints.
The network can have at most one backing vSphere network on each vCenter server registered to the system.
Backing network switches must all be of the same type, either DVSwitch or Standard switch.