Port forwarding when out of the mk NAT

Hi,

Well, I have two separated WANs on my network:
The first WAN is routed through Mktik (enter through the eth1 port and its routed to the lan on eth1) and the second one is through another machine (linux box router).
The second WAN is plugged to mikrotik eth4 port which is bridged and then the eth5 port (also bridged) provides the connection to the linux box (all through mikrotik bridge). I’ve done this bridge salad in order to join one network to another, letting me free to chose any network I want because there are only one cable that goes into the 32 ports switcher that goes to the client machines.

Well, its hard to explain so there’s a simple diagram:

I’ve added the route in my mk to the linux box ip range (192.168.2.X) and the ping is OK (using mikrotik ping tool).

Following the wiki i’ve tried to apply the following port forward firewall rule in my mk:

/ip firewall nat
add action=dst-nat chain=dstnat disabled=no dst-address=200.203.237.1 dst-port=\
    8081 protocol=tcp to-addresses=192.168.2.40 to-ports=8081

…but i think it doesnt work because the returning (response) packages from 192.168.2.40 are lost in the way.
I’ve also tried removing “dst-address=200.203.237.1” and inserting “in-interface=ether1_internet”, but it doesn’t work too.

Any suggestions?
Tks