> My problem is now, that this does not work. Going from the DMZ->WAN always
> is making NAT. Going from the WAN->DMZ does simply not work.

Just for others which might come into the same problem: I got the solution
now. M0n0 is making NAT on every device by default. This means:

> Upstream - Public IP - m0n0 - NAT / 192.168.100.0/24 - LAN
>                          |
>                      194.230.x.0/24
>                          |
>                         DMZ

I have to *enable* enhanced outbound NAT to *deactivate* that default
behaviour and add the 192.168.100.0/24 LAN manually as an outbound NAT
rule and then everything is fine. WAN-DMZ gets routed as wished...

Regards,
Adrian