Deploying BIG-IP Virtual Edition in AWS - trouble with traffic not routing

It seems after reading https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/bigip-ve-setup-amazon-ec2-11-4-0.pdf i may need to add routing to my interface on eth1 . I only have added a single interface and asigned it to 1.1 (external) but no interface for Internal. Do I need to have this configured ? When I created a new VIP and assigned 10.25.8.100 to the VIP I was able to asign the EIP to this VIP address in interface association on the AWS console. Assuming it is a routing issue for the interface 1.1 (external) how does or why do I need a third interface for 1.2 ? Do I associate the node on this interface 1.2 and thr BIG-IP will deal with routing ?