dummy net iface?

Hi guys.

'dummy' network interface - I get that those are meant to be 
kind of a sing/black-hole but... should such iface not 
port-forward on itself? (as oppose to other ifaces, which it 
does not I think)
So, I cannot get "normal" port-forward - firewalld with 
nftables as per default in Fedora, which I try to do it with 
- because it needs more tweaking for "dummy" ifaces _do_ 
port-forwarding or.. they do _not_ - do you know?

many thanks, L.