IPSEC VPN Local cannot reach/ping Remote site without including DMZ segment

[Sulwan_Suliman]

Hi, I have an issue where I create an IPSEC Tunnel to a Cloud server, the tunnel is up but local LAN cannot reach and ping to remote site. After checking the traffic, somehow the traffic is going through the DMZ interface which we currently not using and down. After we add the DMZ IP segment to local address on FortiGate, and add to remote on the Remote cloud, we can reach and ping between the sites. I want to know why it still going through DMZ IP segment even though we are not using the DMZ port and it currently down? Our device is Fortigate 100F, version 7.4.4