How to make port forwarding to the second network in Mikrotik?

Question

Mikrotik

Hello! Please help me understand the following question...
There is a Mikrotik RB2011UiAS-2HnD-IN router, the main local network is 192.168.77.0/24. To access the second network, a patch is plugged into one of the ports of the router from the router to the switch of the second network. The second network is 172.20.10.0/24. The first network has Internet access, the second network does not have Internet access.
The task is to forward one port (8081) through the router of the first network to one of the devices in the second network on port 80.
I do the following:
Through Winbox I go to the interface of the router, in IP - firewall - NAT I add the rule:
chain: dstnat
protocol: tcp
Dst. Port: 8081
I do not touch all other parameters.
Next, on the Action tab, I specify:
Action: dst-nat
To Addresses: 172.20.10.5
To Ports: 80
But for some reason this scheme does not work.
White external IP address is naturally available. Similar rules for devices located in the first network from the 192.168.77.0/24 range work successfully.
Being behind a local PC in the first, the local network of the router, devices from the second network are available. When setting certain settings for the network adapter, naturally, in the form of an appropriate mask, or setting IP and gateway from the second network. In the interface of the router in the IP scanner, devices from the second network are also visible.

Answer 1

In principle, if you don’t want to bother, then just double nat
Wan R0 -> 8081 dst nat -> Wan R1 -> 8081 dst nat to server

Answer 2

Add to your dst-nat rule:
chain=srcnat action=masquerade dst-address=172.20.10.5 out-interface= (the interface to which the wire from the second network is connected)
Well, check that the firewall passes port 80