auto vmbrX
iface vmbrX inet static
address 10.X.X.1/24
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.X.X.0/24 -o <wifi_iface> -j MASQUERADE
post-down iptables -t nat -D POSTROUTING -s 10.X.X.0/24 -o <wifi_iface> -j MASQUERADE