The error "external network is not reachable from the subnet" means that the subnet does not have a route to the external network where the floating IP pool is.

Ensure that you have a router created, your external network set as the gateway, and an interface on the router on the same subnet as the the system you are using.

To do this:

1. Create your router --> In your project tab Click on Network Tab, Go to Routers, Click on +Create Router, Name your router and save
2. Set Gateway --> Click on set Gateway , Select the external network you want., Click on set Gateway.
3. Add Subnet interface --> Click on the routers name, click on + Add Interface, Select the subnet you want to add, add the gateway IP if desired otherwise one will be chosen for you.

At this point you should be able to add the floating IP to your VM.

As per question

i was face the same problem with kilo in ubuntu 14.04 . I was solved the problem related to external communication.I will describe my design .In my environment

I am using vmware esxi 5.5 hyper-visor

I was taken 5 vm to openstack kilo and it was setup it . all are functioning will expect external is not communicating to my external network .For i was search lot of site not result found. i was analysis problem that it was drop the packets from the vmware exsi hyper-visor. To solve the problem

Go to login to vmware esxi vsphere client

Go to configuration setting click on networking --> click on vswitch properties --select vswicth--click edit--click on security --select promiscuous mode --by default it will be in reject mode --- It should be in accept mode then it will work .