In this recipe, we will troubleshoot an infrequent yet very persistent issue that can occur when setting up a VPN connection. When the redirect-gateway directive is used to redirect the default gateway on an OpenVPN client, it sometimes causes the client to lose all the Internet connections. This particularly occurs when the client machine on which OpenVPN is running is connected to the rest of the network or with the Internet using a PPP-based connection, such as PPPoE or PPPoA, especially, when using a GPRS/UMTS connections via a mobile phone.

When this occurs, OpenVPN sometimes is not capable of determining the default gateway before it is redirected. After the default gateway is redirected to the OpenVPN tunnel, the whole tunnel collapses on itself, as all the traffic, including the encrypted tunnel traffic itself, is redirected into the tunnel, causing the VPN to lock up.

This recipe will show how to detect this situation and what can be done...