Networking tutorials for beginners in Hindi Urdu by http://ifactner.com presents Firewalls and Computer Network Security. In this network security tutorial, I introduce the viewer to the concept of firewalls. I discuss software and hardware based firewalls. I discuss the 3 generations of firewalls namely packet filters firewalls, statefull firewalls and application layer firewalls. I mention the OSI model and the respective physical layer, data link layer, network layer, transport layer and application layer in Hindi Urdu language on which these 3 generations of firewalls operate. Later on, I discuss different types of firewalls including packet filters, stateless and stateful firewalls in Hindi Urdu, Application layer firewalls, New generation of firewalls and proxy servers which provide security from the external threats on Internet and extranet. In the end, I mention that firewalls are one of the measures for securing our personal computers and office networks along with Anit virus programmes.