Issue with port forwarding/redirection

Hello All,

Having a small issue and trying to get some help.

We have a web application that runs over port 8100 here internally. I am trying to forward requests so that when someone tries to access the app using http://app.domain.com it will automatically connect to port 80 and therefore not require users to put in :8100 after the url.

So I set this ip in the port fowarding settings, forwarding port 80 to 8100 on that server but for some reason it only works internally. When someone from the outside tries accessing it, it doesnt work.

Oh and I have checked allow hairpin NAT.

Any ideas?

Thanks