FTP server using passive ports

That's basically what I've done. The only problem here is that I need to use ports lower than 1024 to access anything from my work, as they've blocked any port over 1024 on the firewalls.

The setup is like this:

Duo Server

Port: 21
Passive Ports: 14170-14180

Router settings:

Port 21 forwarded from port 21 external to port 21 internal to Duo IP


Ultra Server:

Port: 27
Passive Ports: 14190-14200

Router settings:

Port 27 forwarded from port 27 external to port 27 internal to Ultra IP
Ports 14190-14200 forwarded from port 14190-14200 external to port 14190-14200 internal to Ultra IP



What's strange is that the Duo doesn't use its passive ports, just the normal one, as the Ultra pops in on the passive ports only.

I've also tried changing the portnumber of the Ultra server just to check that it doesn't collide with another service.

Thanks for the answers though