Two ip adresses, one public?

My ISP provides a second vlan with a 10. private network for voice, and it’s meant for ATA’s and such.
My PBX has a connection to my home network to connect to my phones.
I have set up my switching so that it comes into my pbx on a tagged vlan.
I need to do two things:

  1. Set up the tagged vlan in linux network config (DHCP)
  2. I don’t trust this network, what to do firewall wise?
    Help is apreciated.

I have not tested this kind of setup. But.
In System Admin / Network Settings, You can configure your interfaces.
If you have only one physical interface, you can add a virtual interface a select a VLAN.
Next, on the Firewall, you can set your interface to a zone (Ususally Internet Zone).

Go to Connectivity / Firewall / Interfaces, and change the zone for each one interfaces. Internet Zone is the good one.