LACP with 2 NICs working when either one is down, not when both are up
Solution 1:
The only LACP config I managed to get working in Ubuntu is this:
auto bond0
iface bond0 inet dhcp
bond-mode 4
bond-slaves none
bond-miimon 100
bond-lacp-rate 1
bond-updelay 200
bond-downdelay 200
auto eth0
iface eth0 inet manual
bond-master bond0
auto eth1
iface eth1 inet manual
bond-master bond0
i.e. I don't use bond-slaves but bond-master. I'm not sure what the difference is but I found this config worked for me.
I don't have any issues with LACP under my setup although this is with 1Gbe networking.
In addition, if you're still getting problems, try plugging both cables into the same switch and configuring the ports for LACP. Just to eliminate the possibility of issues with multi chassis LACP.