LEDE with external Raspberry VPN-Gateway

Dear all,

it's my first post because i'm becoming crazy to configure my home.network with external Raspberry VPN.

Situation:
Main-Router with LEDE (192.168.1.1)
Secondary DD-WRT-Repeater connecting via WLAN to LEDE (192.168.1.200)

The Main-Router is acting as DHCP-server. All clients connecting via the repeater get an IP from the Main-Router.

Problem:
I installed and configured a Raspberry Pi3 with openVPN connecting to PrivateInternetAccess. The connection is running without problems. The raspberry is connected via LAN to my Main-Router.

  1. I configured my mobile to connect to the WLAN of my Main-Router including static ip and use the RaspberryPI3 as Gateway and DNS-Server

    no problem (Mobile gets the IP of the VPN-connection)

  2. When i configure the same mobile with the WLAN of the Repeater including static IP and the use of the RaspberryPI3 as Gateway and DNS-Server

    The mobil is using the normal internet-connection of the Main-Router instead of the Raspberry-VPN

  3. When connecting a device via LAN to my Repater pointing to the VPN (Gateway + DNS)

    no internet-connection available

Just before is used openVPN on the Main-Router causing the whole traffic to go over the VPN. Due to low performance i had to work with iptables to get some IP's out of the VPN which is very hard to configure. Therefore i decided to use a Raspberry as VPN-Gateway. I can just configure the devices i want to have in the VPN-tunnel.

Question:
How can i ensure that all devices being configured to use the VPN-gateway really use it instead of the Main-Router independend whether they're connected vi WLAN/LAN from the repeater ?????

Thanks in advance for your support !

KN
available