@Christophe \Can you please explain what you mean by "no communication is possible with the various instances that are runned by OpenStack (or the attached router)". By "various instances" are you referring to VMs connected to the same network? Please elaborate. I would like to reproduce the problem.
@Christophe \Can you please explain what you mean by "no communication is possible with the various instances that are runned by OpenStack (or the attached router)". By "various instances" are you referring to VMs connected to the same network? Please elaborate. I would like to reproduce the problem.