Disclaimer: Officially, with version 10.03 this method is not supported

Limitations Remote installation of clients across a firewall is not supported. You need to install clients locally in the DMZ. This setup does not allow the backup of databases or applications using Application Agents on clients in the DMZ.

However, I was able to figure out the prerequisites to make it work.

Here is what you need to do:

• On the server you want to backup, give the Logon as a service right to the account used for the installation
  If you want to do it the PowerShell way, you can give a try to a module made by Tony and which you can find on the Microsoft Gallery
• Open following ports on both your computer’s firewall and on the network firewall
  

  Source computer	Source port	Destination computer	Destination port	Usage
  Cell Manager	Dynamic (49152 – 65535)	Disk Agent from the computer to backup	5555	Upgrades
  Cell Manager	Dynamic (49152 – 65535)	Disk Agent from the computer to backup	5556	New installation
  Disk Agent from the computer to backup	Dynamic (49152 – 65535)	Cell Manager	139 and 445	Access to sources on the installation share

That’s it!
Now you can add and update your clients from the Data Protector Manager console like you do it with your LAN computers.

Note

Ports listed above are used for the installation, but port 5555 and 5556 are also used by the Cell Manager to ask the computer to start the backup.

They are also used the other way by the Disk Agent from the computer you want to backup to reestablish a broken communication with the Cell Manager.

In Addition, you must also open ports from the computer to backup to the Media Agent which is connected to a storage device.

More about

Prepare for installation (Micro Focus Docs)

Firewall support (Micro Focus Docs)
On the left unfold Firewall Support and you will see three subpages.