3.1  Configuration of network interfaces of the Internet gateway

Set a fixed IP address (e.g. 10.1.1.1) at the firewall's interface connected to the local network. Set the same IP address as the primary DNS server (this ensures that also DNS queries from the local host will be forwarded to the DNS Forwarder — this is important especially in case that dial-up connection is used). Make sure that no default gateway is set on this interface!

Follow the ISP's instructions to set the interface connected to the Internet.