/etc/network/interfaces

auto WRLDbr
iface WRLDbr inet static
         bridge-ports none
         bridge_fd 0
         bridge_hello 0
         bridge_stp off
         #
         address 192.168.100.1
         netmask 255.255.255.0
         gateway 192.168.100.1
         sysctl net.ipv4.ip_forward=1
         #
         post-up iptables -t nat -F
         post-up  iptables -t nat -A POSTROUTING -s 192.168.100.0/24 -o eth0 -j MASQUERADE
         #
         post-down iptables -t nat -F

auto PRIVbr
iface PRIVbr inet static
     bridge-ports none
         bridge_fd 0
         bridge_hello 0
         bridge_stp off
         #
     address 10.0.10.1
     netmask 255.255.255.0
         # gateway 10.0.10.1
         sysctl net.ipv4.ip_forward=1