Chapter 12 Load Balancing for FortiOS 5.0 : Configuring load balancing : Load balancing overview : Health check monitoring : Virtual IP, load balance virtual server and load balance real server limitations
  
Virtual IP, load balance virtual server and load balance real server limitations
The following limitations apply when adding virtual IPs, Load balancing virtual servers, and load balancing real servers. Load balancing virtual servers are actually server load balancing virtual IPs. You can add server load balance virtual IPs from the CLI.
Virtual IP External IP Address/Range entries or ranges cannot overlap with each other or with load balancing virtual server Virtual Server IP entries.
A virtual IP Mapped IP Address/Range cannot be 0.0.0.0 or 255.255.255.255.
A real server IP cannot be 0.0.0.0 or 255.255.255.255.
If a static NAT virtual IP External IP Address/Range is 0.0.0.0, the Mapped IP Address/Range must be a single IP address.
If a load balance virtual IP External IP Address/Range is 0.0.0.0, the Mapped IP Address/Range can be an address range.
When port forwarding, the count of mapped port numbers and external port numbers must be the same. The web‑based manager does this automatically but the CLI does not.
Virtual IP and virtual server names must be different from firewall address or address group names.