How to forward virtual machine traffic through VPN?

Question

Computer networks

Please tell me how to make this wish come true.
There is a Host (Proxmox), on it is a virtaulka. External ip 123.123.123.123. The virtual machine is spinning inside 10.0.0.0/24.
On the host, we start the OpenVPN client (tun0, 10.18.0.0/24) with the redirect-gateway disabled.
It is necessary to force all traffic from the virtual machine and back through the VPN, but only this traffic.
You cannot touch the virtual machine (inside, i.e. run the OpenVPN client inside the virtual machine).
Host config:

iface eno1 inet manual
auto vmbr0
iface vmbr0 inet static
        address  123.123.123.123/24
        gateway  123.123.123.1
        bridge-ports eno1
        bridge-stp off
        bridge-fd 0

auto vmbr1
iface vmbr1 inet static
        address  10.0.0.1
        netmask  24
        bridge-ports none
        bridge-stp off
        bridge-fd 0
post-up         iptables -t nat -A POSTROUTING -s '10.0.0.0/24' -o vmbr0 -j MASQUERADE

Tried iptables -t nat -A POSTROUTING -s '10.0.0.0/24' -o tun0 -j MASQUERADE
but something is missing...

Answer 1

Found the solution myself:

iptables -A FORWARD -i vmbr1 -o tun0 -j ACCEPT
iptables -A FORWARD -i tun0 -o vmbr1 -j ACCEPT
iptables -t nat -A POSTROUTING -o tun0 -j MASQUERADE
echo 100 vguest >> /etc/iproute2/rt_tables
ip rule add from 10.0.0.0/24 table vguest
ip route add default dev tun0 table vguest

Answer 2

iproute2 is able to work with the traffic marked through iptables.
Mark the traffic in the PREROUTING table via iptables -j MARK --set-mark as you need, then pick it up with iproute2 and route it as you need.

Answer 3

Through iptables this task is not solved. At all.
Solved through tricky routing:
https://www.google.com/search?q=source+based+routing
https://habr.com/ru/post/108690/

Answer 4

function calculate($number, $counter = 0)
{
    $result = $number + $number / 100 * 30;
    storeResult($result);
    
    if ($counter < 800) {
        calculate($result, ++$counter);
    }
}

Answer 5

$a=20; //input number
for($i=0; $i<=800; $i++){
$a+=($a/100*30);
$a=round($a);
echo $a.'
'; //write to database
}
but where did you learn to write $a=$a+... instead of $a+=... and $a=explode('.', $a); $a=$a[0]; instead of $a=round($a); ? And besides, you don’t understand cycles.
I wonder how you then know how to write to the database. Probably leafed through the textbook in search of the necessary functions. Don't repeat my mistakes. He did the same thing - now he's a govnokoder. The textbook should be read from cover to cover, and not selectively. You will only get better for it.