Using a 'learn-address' script

This recipe will demonstrate how to set up a learn-address script that is executed on the server side when there is a change in the address of a connecting client. Learn-address scripts can be used to dynamically set up firewalling rules for specific clients or to adjust routing tables.

In this recipe, we will use a learn-address script to open up a firewall and to set up masquerading for a client. When the client disconnects, the firewall is closed again and the 'iptables' masquerading rule is removed.

Getting ready

Install OpenVPN 2.1 or higher on two computers. Make sure the computers are connected over a network. Set up the client and server certificates using the first recipe from Chapter 2. In this recipe, the server computer was running CentOS 5 Linux and OpenVPN 2.1.1. The client was running Windows XP SP3 and OpenVPN 2.1.1. For the client, keep the client configuration file basic-udp-client.ovpn from the Chapter 2 recipe Using an 'ifconfig-pool' block...