It is more a security question, i.e. your firewall wont let to connect from your intranet server with
Kentico 6 to outside (internet) server.
Not the best picture, but normally your company www servers for internet users located in the DMZ, all other servers on LAN.
Technically all request from internet can go to DMZ and back, but not to LAN. Again depends on your network set up, firewall rules etc, you have to ask your admin.