ping to floating IPs of VMs start working only after pinging from within VM to the outside first

Pinging floating IP of a VM on overcloud from an external machine doesn't work straight away. It starts working only after pinging from within VM to the outside/external world first.

Steps to Reproduce:
1. create a VM, assign a floating IP to it
2. test ping from a machine on external network to this VM's floating IP doesn't work. After logging in to the VM and the external vm ,the originally failing ping external to VM starts to work as well.