Setting up a private network

I'm new to networking and linux so I apologize if some of these questions have obvious answers. I'm trying to set up something that looks like this: ~~[http://code.mixpanel.com/wp-content/uploads/2010/09/network.png" target="_blank">](http://code.mixpanel.com/wp-content/upl … etwork.png">http://code.mixpanel.com/wp-content/uploads/2010/09/network.png](. I have my OpenVPN server running and I can ping what will be the server housing my API with the IP OpenVPN sets 10.8.0.5, for example. The API server is currently a client of the VPN server but also allows public traffic. I want to be able to SSH into my private servers which I'm doing through tun0 but aside from that I only want other servers within the network to be able to speak to each other. In other words, the API server should only be able to speak to the Web server (which will be external facing) and the DB server (which won't be external facing).

The image I linked to above is from this article ~~[http://code.mixpanel.com/2010/09/08/openvpn-in-the-rackspace-cloud/" target="_blank">](http://code.mixpanel.com/2010/09/08/ope … ace-cloud/">http://code.mixpanel.com/2010/09/08/openvpn-in-the-rackspace-cloud/]( which mentions using eth1. From what I can tell Linode doesn't provide eth1. Any guidance on the next steps I need to take? Is it just a question of adding some iptable rules on the API server?