Answer by zioproto for I've deployed Openstack using RedHat's Packastack allinone option on Centos7. I then followed the instructions at https://openstack.redhat.com/Neutron_with_existing_external_network to use my existing external network. Next, I created a private network for the admin project with a range of 192.168.13.0/24. I then started up a guest in the admin project, and it was allocated an IP from this range (192.168.13.2). However, when I come to associate a floating IP with this guest so that I can access it internally, I am receiving a message saying "No Ports Available". I am able to select an IP address from the pool that I setup when following the document above. Can anyone advise what I have to do in order to complete this setup and map floating IPs to my compute instances on the private network please ?

You need to create a router in your tenant. The router should have 1 interface in the private network you created and you should also set the gateway for the router in the external network. After these steps you will be able to assign floating IPs to instances from the web interface.