root@:~# sysctl net.ipv4.conf.all.forwarding
net.ipv4.conf.all.forwarding = 1

root@n:~# cat /etc/network/interfaces
auto lo
iface lo inet loopback

iface eno1 inet manual

iface eno2 inet manual

auto vmbr0
iface vmbr0 inet dhcp
       bridge-ports eno1
       bridge-stp off
       bridge-fd 0

auto vmbr1
iface vmbr1 inet static
        address 10.0.0.1
        netmask  255.255.255.0
        bridge-ports none
        bridge-stp off
        bridge-fd 0

        post-up echo 1 > /proc/sys/net/ipv4/ip_forward
        post-up iptables -t nat -A POSTROUTING -s 10.0.0.0/24 -o vmbr0 -j MASQUERADE
        post-down iptables -t nat -D POSTROUTING -s 10.0.0.0/24 -o vmbr0 -j MASQUERADE