Web Dispatcher - Which Ports needs to be opened?

Hi experts,

we want to open an SSL Connection from WebDispatcher to ABAP-System.

As far as I know, I need to open the MSG-http port (80##) and the ICM-https Port for this in DMZ.

At least for a JAVA-System this is enough.

Now I did figure out, that for a ABAP-System also the ICM-http Port needs to be opened.

Is this correct, so that for a ABAP system I have to open also the http port if I want to make a trusted connection?

(if I don't open it, I get a "Server is not reachable").

Kind regards