Let's say I want to access a server on port 5901 in the internal network but rom the outside network, I want to connect to port 5900.
So it may look like this: 5900 => 5901
STEP 1: Create new custom service.
Create new service: RedirectExtPort on TCP 5901.
STEP 2: Add firewall-access-rule.
Firewall -> Access Rules
WAN -> LAN
Service: RedirectExtPort
Source: Any
Destination: WAN IP
STEP 3: Add NAT Policy
go to Network -> NAT Policies
New Policy:
Original Source: Any
Translated Source: Original
Original Destination: WAN IP
Translated Destination: InternalServerIP
Original Service: RedirectExtPort
Translated Server: RDP5900
Inbound Interface: WAN Port
Outbound Interface: Any