The LAN firewall is a multi-tasker "device" (A) A firewall monitors, inspects and controls inbound and outbound LAN traffic. (B) It makes use of user-defined preferences to allow and deny communication with a specific network. These preferences point out the criteria and the features by which the firewall decides to allow or don't the network traffic. Packets are checked to examine their purposes. If the content looks suspicious and intends to make illegal attempts, then the firewall will immediately block them. (C) The firewall also checks the sender's I.P. address. The firewall deletes the packets without even looking through them. If it is an unknown I.P. address and the firewall is set accordingly, it will automatically bar the entry of the packets. (D) Network firewalls are also used to isolate PC's belonging to a particular network from other networks. To be even more precise, this firewall can also compartmentalize subnetworks within a huge corporation network. To zoom in even further, the network firewall can also be used to keep a private network separate from the web. Network firewalls are crucial in isolating your network from others that you want to limit or control communication with. A comparison from daily life may make the explanation simpler. A firewall can be compared to a family dog that only recognizes and allows family members and friends to enter the house, while keeping strangers at bay. Or a firewall can be compared to a bodyguard. This firewall bodyguard knows when to allow someone to approach you and when not to allow someone to approach you. However you want to look at it, a firewall is an essential piece of hardware or software, or combination thereof (in whatever form you use)to keep your PC and network safe from intruders.