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.