How to set up your FortiWeb : Planning the network topology : How to choose the operation mode
 
How to choose the operation mode
Many things, including:
supported FortiWeb features
required network topology
positive/negative security model
web server configuration
vary by the operation mode. Choose the mode that best matches what you and your customers need. Considerations are discussed in “Supported features in each operation mode” and “Matching topology with operation mode & HA mode”.
Because this is such a pivotal factor, consider the implications carefully before you make your choice. It can be time-consuming to reconfigure your network if you switch modes later.
 
If you are not sure which operation mode is best for you, you can deploy in offline protection mode temporarily. This will allow you to implement some features and gather auto-learning data while you decide.