The increasing spreading of the amount of exchanging data and the dynamic deployment of applications and services lead to an evolution of the traditional network technology. One possible solution is based on virtualization, in particular exploiting the Network Function Virtualization (NFV) parading. It is an architectural approach which aim is to decouple the network functions and the hardware appliances, making possible the deployment of network service on general purpose servers, achieving flexibility during the design of a particular service. A problem that arises is the service design that usually is performed manually, and this can lead to errors, especially if the service under analysis is related to security function, such as firewalls.