Once the client IP_FORWARDING on the OpenVPN client has turned on, a client-side network access is possible. Access only to the OpenVPN client does not require IP_FORWARDING.
IP_FORWARDING is necessary to enable the network behind the client (Road Warrior) for the OpenVPN servers network.
The activation of the IP Forwarding (IP_FORWARDING) works as follows:
IP_FORWARDING on Windows 7 client side
This was tested with Windows 7:
To enable the IP forwarding (that means to enable the routing), you have to go into the Windows Registry, click on Start → Run and type regedit. Now navigate to the key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
and then change the entry IPEnableRouter from 0 to 1. After modification restart the machine. Now the client can offers his subnet to OpenVPN.
IP_FORWARDING on Linux client side
A check out if IP_FORWARDING is already activated, can be done with the following command:
cat /proc/sys/net/ipv4/ip_forward
if the answer is a 0 it is deactivated, by an answer of 1 it is activated .
For a temporarily activation of ip_forwarding the following command can be used:
sysctl -w net.ipv4.ip_forward=1
A permanent ip_forwarding should be made with this command:
echo 1 > /proc/sys/net/ipv4/ip_forward