I have a 871 router having few vpn's on it i have to redirect a port of remote desktop on it so ppl from outside can access my my system which is on the internal interface of router and my system has private ip on it
ip nat inside source static tcp . The outside IP is from the outside interface of the router or that subnet.
ip nat inside source static tcp 192.168.13.100 3389 interface 18.104.22.168 9833
From the outside a user would connect to 22.214.171.124:9833 in remote desktop. When it hits the router, the router will translate it to the the inside server 192.168.13.100 on port 3389.
HTH and please rate.