auto vmbr1
iface vmbr1 inet static
        address  100.64.43.1
        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 '100.64.43.0/24' -o eth0 -j MASQUERADE
        post-down iptables -t nat -D POSTROUTING -s '100.64.43.0/24' -o eth0 -j MASQUERADE