Trunk with F5

If you are creating etherchannels on the Cisco switches, both pieces of cable have to go to the same BIG-IP.

 

 

If that isn't what you are doing, then you shouldn't put 1.1 and 1.2 on the BIG-IP in a trunk, just assign them both to the same vlan, make sure they are assigned the same vlan on each switch, make the trunk between switches an L2 bridge and let spanning tree do the rest.