Chapter 4 FortiOS Carrier : Carrier web-based manager settings : GTP Profile : Message type filtering options
  
Message type filtering options
On the New GTP Profile page, you can select to allow or deny the different types of GTP messages, which is referred to as message type filtering. You must expand the Message Type Filtering section to access the settings.
The messages types include Path Management, Tunnel Management, Location Management, Mobility Management, MBMS, and GTP-U and Charging Management messages.
 
For enhanced security, Fortinet best practices dictate that you set Unknown Message Action to deny. This will block all unknown GTP message types, some of which may be malicious.
To configure message type filter options, expand Message Type Filtering in the GTP profile.
See also 
General settings options
APN filtering options
Basic filtering options
Advanced filtering options
Information Element (IE) removal policy options
Encapsulated IP traffic filtering options
Encapsulated non-IP end user traffic filtering options
Protocol Anomaly prevention options
Anti-Overbilling options
Log options