List of connected IP to a router

Hi all,

I'm using a fortigate unit with Ipv4, IP are manually entered in every-one's computer. 

I have two interfaces, (1) with 10.18.x.x IP and (2) with 172.25.1.x IP. Im suspecting an IP conflict occured on the 172.21.1.x range but when I go to the Fortigate administration panel, User & Device > Device > Device Definition,  no devices connected to the interface (2) are shown, when there are at least three servers.

Where can I find information about the devices connected to my interface (2) (or actually every interfaces) ?

I access the administration panel with a computer connected to interface (1), I don't know if it's relevant.

Thanks,