The public IP at ETH04 is from the former/later location. There is a range of pulic IP’s.
The private IP is at my home where i troubleshoot the balancer.
ETH03 is my lan with one gateway machine. This machine and the balancer itself should be reachable over the virtual servers.
My perception of the GUI Router/NAT was, that one has to point to the both devices between NAT is supposed to be. This was obviously wrong. Additionally behind the curtain works MASQUERADING and not NAT. This is confusing too.
After some testing MASQUERADING only on device ETH04 solves the Problem.
In virtual servers also the IP wich is supposed to be used has to be configured explicitly.
Configuring the device only does not work.
I thank you for your effort and the hint about MASQUERADING.