Got this kind of noob question i suppose. I got this very basic network setup and need help to set up some address forwarding.

As seen in my illustration below all traffic enters via the eth0 interface (85.123.32.23). The external dns is setup to direct all hosts to this ip as well.

Now, how on earth do I filter the incoming requests to each box? The Ip's are static!

My network layout:

I do not wish to solve this by assigning tons of ports etc.

In my wishful thinking something like this would be nice :)

set service nat rule 10 type destination
set service nat rule 10 inbound-interface eth0
set service nat rule 10 destination address ftp.myhost.com
set service nat rule 10 inside-address address 192.168.100.20

This way ALL traffic to the address ftp.myhost.com (at eth0) should be routed to the internal ip, 192.168.100.20.

Right, is there anyone who could point in some direction? Maybe it's wrong to use nat?

Please help me! :)