In the external networking case, every VM in a zone must have a unique guest IP address. There are two variables that you need to consider in determining how to configure CloudStack to support this: how many Zone VLANs do you expect to have and how many VMs do you expect to have running in the Zone at any one time.

Use the following table to determine how to configure CloudStack for your deployment.

Based on your deployment's needs, choose the appropriate value of guest.vlan.bits. Set it as described in Edit the Global Configuration Settings (Optional) section and restart the Management Server.