The following setup works fine on a Debian Lenny system. Notice also that the same setup on a Ubuntu 9.04 server causes a kernel panic!
The machine is a SUN blade server with two NICs. Each NIC is connected to a different switch in a redundant manner. These are the contents of the
auto lo iface lo inet loopback auto bond0 iface bond0 inet manual slaves eth0 eth1 bond_mode active-backup auto br0 iface br0 inet static address 192.168.11.20 netmask 255.255.255.0 network 192.168.11.0 broadcast 192.168.11.255 gateway 192.168.11.1 bridge_ports bond0