I have a doubt. IP addresses of the PCs connected to this network do not seem to change every time they connect to the network. I should tidy up the IP addresses, respecting the physical layout of the PC. The firewall is a fortigate 90d, while the firmware version is v5.0
I post a picture, to understand how the network is set:
--UPDATE--
I tried to reserve an IP address, but the PC network card fails to obtain the ip: