Currently on the market more common 3、4Layer firewalls，Called the network layer firewalls，There Layer 7 firewall，In fact, the gateway proxy layer
forTCP/IPofSeven-layer modelSpeaking，The third layer is the network layer，Three-layer firewall in this layer of the source and destination addresses for testing。But for the seven firewalls，Whether you source port or destination port，What is the source or destination address，We will have to check all your stuff。[……]