iDirect 3100 Configuration for VPN Deployment

PLEASE HELP ME ON THIS:

We have an iDirect 3100 satellite router installed by our ISP. As i understand, the iDirect 3100 is being used as a NAT server beacuse when they installed it, there was a linux server directly connected to it with an IP address of 10.11.100.2, gateway-10.11.100.1 and that linux served as DHCP for the workstations with 192.168.75.0/24 subnet.

After some time, I decided to replace the linux dhcp server with the Netgear FVS336G VPN Firewall hoping to deploy VPN in the future. I have read the manual of our new VPN firewall and tried to explore ways to implement VPN but no luck.

These are my questions:

1. Is it needed to configure the iDirect for VPN? (port triggering or something) because I don't know the configurations of the iDirect and our service provider is sort of reluctant to help me.

2. What ports are to be forwarded to 10.11.100.2 (Netgear) to be able to deploy VPN?

3. Can you please give me the step by step process for the FVS336G to have a secure VPN?

Thank you.