Enabled on you external firewall? I still don't really have a clue how you have set things up over there. My best guess is something like this.
Code:
(Inernet)----(Router)-----(Apache Server)
(0.0.0.0) (81.X.X.X) (Private IP)
Something like that? If you have only one static IP then you'll be masquerading your server using a private IP.