Recently I worked on a network installation using Fortinet 200A firewalls. During the process of getting BGP operational with the colo provider they requested information about or BGP prefixes. They requested that we provide the output to “sh ip bgp” or “show ip bgp” to them.
Short Answer: get router info bgp network (From the console window or the CLI)
The easiest way to get this information is to connect to the console via the firewall admin GUI and issue the command “get router info bgp network”. If SSH access is turned on then you can SSH to the firewall and issue the same command.