In transparent mode, the FortiADC appliance (the load balancer) splits a subnet into two VLANs and bridges them together. This allows you to insert the appliance into an existing network without modifying the IP addressing.
To support deploy FortiADC in transparent mode, you must first create a softswitch interface on the appliance. All traffic that FortiADC does not supported can directly pass through this soft-switch interface without interruption, and FortiADC-supported traffic, such as LLDB and DHCP, needs to be terminated.
Keep in mind that the FortiADC soft-switch does not participate in the STP node, and all STP BPDU will be forwarded by this soft-switch interface directly.
For more information, see FortiADCTransparent Configuration Guide.