|I little bit confusing... I will help with an example..|
A and B are systems on LAN .. ( Let it be your office ) with R1 as ADSL/router, Static WanIP-W1
C is systems is somewhere not on LAN ,( let it be your home )
Our target rdp to A from C
now you can rdp A from B, Yes
But you cannot rdp from C
Now here is your process. In router R1 you need to port forward 3389 to A ( local IP Address and not Wan IP ). As when you do rdp from B to A you are giving Local Ip Address . The system a listening of Port 3389 on LAN IP.
Now sitting at C you will do RDP to Static WAN IP : W1
Suppose you do not have a static wan-ip at office and you have a dynamic , means which changes frequently, then when you will try to connect from C to A another other time , it will not connect as the WNA IP W1 would have changed to W2 or any other. So in such cases you need to have W2 value now ( changed WAN-IP ).
So it will be difficuilt for you to track these manually each time. To overcome this issue you should open a free account at Dyndns.com ( it is free for 2 IP tracks ).
Now inside DYNDNS.COM register a name for your office location eg office.dyndns.org.
In router there will be an entry of DDns , put your username/password and host name . Username is: account name at dyndns.com , password you gave to register , hostname is office.dyndns.org
So when ever you ip address of router changes it will automatically update office.dyndns.org .
So whenever you now do rdp to A sitting at C , you will just give office.dyndns.org to do rdp ( which will automatically resolve the WAN-IP of your office )