I'm having the following configuration:

Windows 7 hosting VirtualBox and it's guest: Ubuntu

The machine (physical) which runs VirtualBox is behind the router and has the address of 192.168.0.110

VirtualBox runs the Bridged network, and the IP of VirtualBox-ed Ubuntu (eth0) is 192.168.0.200

Host (Win7) is running HTTP service on port 80, while guest (Ubuntu) is running it's service on port 9000

I can access both services from inside the network by typing the ip_address:port and this works fine.

Both ports are forwarded on the router to their's respective IPs:

80   -> 192.168.0.110:80
9000 -> 192.168.0.200:9000

Unfortunately, accessing the router's external IP doesn't work as expected. While external_ip:80 works correctly, external_ip:9000 - doesn't

I believe the problem is VBox - related, since the same network is running also other physical machine with Ubuntu and http service on 8000 and this one is forwarded correctly.