Comment 6 for bug 690433

@David,

Maybe adding a "post-up" command to your bridge configuration in /etc/network/interfaces would help. Here is an example :

# The primary network interface
auto br0
iface br0 inet static
    address 172.16.20.1
    netmask 255.255.255.0
    gateway 172.16.20.2

    # Workaround for upstart problem
    post-up /sbin/sysctl -p /etc/sysctl.d/60-bridge-firewalling.conf