How to set up a VPN Range

Hello Guys,

I have installed Tomato 1.28
Now I have just a short question regarding to set up a working IP range in combination with Open VPN Client.

I have setted up a working Open VPN Client with AES-256 CBC.
But it seems when the router reboots it is a short time connected with the real IP instead the VPN.
Is it a way to set up an IP range to allow only IP from my VPN provider, because other way its no more so secure?

Thank a lot

Gandor