Ok I have setup a VNC server, I have port forwarded TCP/UDP for both 5900 and 5800. Everything works fine all ports are open according to (http://canyouseeme.org/). But i still cannot access it using the external ip address. It works fine with the internal ip address but somehow not the external. Any ideas?
You'll need a router that supports hairpin NAT (sometimes called "lookback NAT", a form of dual NAT where both the source and destination addresses are rewritten) to access a forwarded service from the inside using the outside IP address. This answer explains why port forwarding won't work unless the connection originates from the Internet side of the router. Most SoHo routers can't do loopback NAT with their factory firmware.