There can only be one DMZ host. If some software needs to open a port, port mapping is still needed. Generally, you can specify the port number in the downloaded software and set it directly in the router to directly connect to the Internet
According to my experience, the IP in the form of 192.168. * * *. * * * is an intranet IP. Since three machines share an internet IP, when the DMZ is mapped, the internet IP will be distributed to specific computers, that is, corresponding to your "192.168.1.9", and it does not need to be so complicated
