Port forwarding to IP belonging to another gateway

So…
RED network subnet
192.168.30.1 Router
192.168.30.2 PBX (router as gateway)
192.168.30.3 NethServer RED interface (router as gateway)
GREEN network subnet
Subnet unknown
Any computer into GREEN subnet should access to 192.168.30.2 flawlessly…

Yes it is: if you cannot manage the router in any way, call ISP and ask fo port forwarding

  • to PBX
  • to NethServer

for every service that you need
My question is: are you sure you want your PBX admin console reachable from every public ip address of the world?
There are two options to avoid this, IVMHO

  • Enable RoadWarrior OpenVPN on NethServer
    Ask ISP to forward port used by RoadWarrior OpenVPN
    Push route to PBX/RED into OpenVPN configuration
    Create a firewall to access OpenVPN->PBX and Viceversa (maybe optional)
    Connect from WAN with OpenVPN and check PBX access

Or

  • Reconfigure PBX and put into GREEN Subnet
    Ask ISP to forward port used by PBX admin console to NethServer
    Configure portforward and FIrewall rule on NethServer conditioned to Time and public ip Addreses