How to forward routes for Double OpenVPN?

Question

linux

There is a router. Goes online through the so-called Russian PPPOE.
The OpenVPN client and server are also raised on it.
The client connects to another OpenVPN server that I don't have access to.
The task is this.
1) For OpenVPN Client to knock on another OpenVPN server directly via the Internet.
2) Make it so that the OpenVPN Server on the router sends / receives packets through the OpenVPN Client.
3) All users that are connected to the router via Wifi or Lan directly without OpenVPN got to the Internet in a standard way, that is, through Russian PPPOE ignoring the OpenVPN Client. And those who connect via OpenVPN followed point 1.
There are interfaces on the router. Where tun0 is OpenVPN Server and tun1 is Client. eth0 - provider's locale, ppp0 - access to the Internet.

eth0       Link encap:Ethernet  HWaddr 08:60:6E:71:B1:FE
           inet addr:172.18.4.130  Bcast:172.18.4.255  Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:8914 errors:0 dropped:0 overruns:0 frame:0
           TX packets:10659 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:4665579 (4.4 MiB)  TX bytes:4933303 (4.7 MiB)
           Interrupt:4 Base address:0x2000

eth1       Link encap:Ethernet  HWaddr 30:5A:3A:72:7B:D0
           UP BROADCAST RUNNING ALLMULTI MULTICAST  MTU:1500  Metric:1
           RX packets:2929 errors:0 dropped:0 overruns:0 frame:6482
           TX packets:4220 errors:1 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:449782 (439.2 KiB)  TX bytes:692048 (675.8 KiB)
           Interrupt:3 Base address:0x8000

eth2       Link encap:Ethernet  HWaddr 30:5A:3A:72:7B:D4
           UP BROADCAST RUNNING ALLMULTI MULTICAST  MTU:1500  Metric:1
           RX packets:238 errors:0 dropped:0 overruns:0 frame:43
           TX packets:1876 errors:1 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:77690 (75.8 KiB)  TX bytes:273883 (267.4 KiB)
           Interrupt:5 Base address:0x8000

lo         Link encap:Local Loopback
           inet addr:127.0.0.1  Mask:255.0.0.0
           UP LOOPBACK RUNNING MULTICAST  MTU:16436  Metric:1
           RX packets:269 errors:0 dropped:0 overruns:0 frame:0
           TX packets:269 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:51302 (50.0 KiB)  TX bytes:51302 (50.0 KiB)

ppp0       Link encap:Point-to-Point Protocol
           inet addr:109.200.200.209  P-t-P:210.230.0.200  Mask:255.255.255.255
           UP POINTOPOINT RUNNING MULTICAST  MTU:1492  Metric:1
           RX packets:4294 errors:0 dropped:0 overruns:0 frame:0
           TX packets:2987 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:3
           RX bytes:3711004 (3.5 MiB)  TX bytes:680220 (664.2 KiB)

tun0       Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-0                                                                                                                                                              0-00
           inet addr:10.8.0.1  P-t-P:10.8.0.1  Mask:255.255.255.0
           UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

tun1       Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-0                                                                                                                                                              0-00
           inet addr:10.12.248.93  P-t-P:10.12.248.93  Mask:255.0.0.0
           UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
           TX packets:1 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:0 (0.0 B)  TX bytes:40 (40.0 B)

vlan1      Link encap:Ethernet  HWaddr 30:5A:3A:72:7B:D0
           UP BROADCAST RUNNING PROMISC ALLMULTI MULTICAST  MTU:1500  Metric:1
           RX packets:3470 errors:0 dropped:0 overruns:0 frame:0
           TX packets:5590 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:702107 (685.6 KiB)  TX bytes:3981627 (3.7 MiB)

vlan2      Link encap:Ethernet  HWaddr 30:5A:3A:72:7B:D0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

ip route

192.168.1.1 via 172.18.4.1 dev eth0  metric 1
192.168.1.115 via 172.18.4.1 dev eth0  metric 1
94.242.216.66 via 213.231.0.200 dev ppp0
194.143.136.5 via 172.18.4.1 dev eth0  metric 1
213.231.0.200 dev ppp0  proto kernel  scope link  src 109.200.200.203
192.168.1.11 via 172.18.4.1 dev eth0  metric 1
172.18.54.0/24 dev eth0  proto kernel  scope link  src 172.18.4.13
10.8.0.0/24 dev tun0  proto kernel  scope link  src 10.8.0.1
192.168.1.0/24 via 172.18.4.1 dev eth0  metric 1
192.168.0.0/24 dev br0  proto kernel  scope link  src 192.168.0.1
172.18.0.0/16 via 172.18.4.1 dev eth0  metric 1
172.19.0.0/16 via 172.18.4.1 dev eth0  metric 1
172.17.0.0/16 via 172.18.4.1 dev eth0  metric 1
10.0.0.0/8 dev tun1  proto kernel  scope link  src 10.12.248.93
127.0.0.0/8 dev lo  scope link
0.0.0.0/1 via 10.255.255.254 dev tun1
128.0.0.0/1 via 10.255.255.254 dev tun1
default via 210.230.0.200 dev ppp0
default via 172.18.4.1 dev eth0  metric 1

Answer 1

10.12.248.93/8
10.8.0.1/24
well, first of all, set up your OpenVPN server, the address is in a different subnet,
but in general,
ip rule add from 10.8.0.0/24* lookup 100
* -change to a new one
ip route add default via 10.255 .255.254 dev tun1 table 100
iptables -t nat -A POSTROUTING -o tun1 -j MASQUERADE