On debian squeeze, I setup a bridge based on eth0. My /etc/network/interfaces is
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
#allow-hotplug eth1
#auto eth0
iface eth0 inet manual
iface eth0 inet6 manual
auto br0
iface br0 inet dhcp
bridge_ports eth0
bridge_stp off
# bridge_maxwait 0
bridge_fd 9
bridge_hello 2
bridge_maxage 12
Despite setting eth0 to manual, it get's an ip address via DHCP. Setting ifconfig eth0 down explicitly, disables the interface for a few seconds before it comes back up again.
How can I disable eth0 and use br0 has my only network interface?
/var/log/*, look for files modified around the time the network came up) for clues.