How does a firewall work???

The other important aspect of computer security is a firewall. Those who use the computers would have heard the term firewall. Firewall acts as a barrier which keeps checking the incoming as well as the outgoing packets. These packets are usually checked for security breach. That is why it has got the name as firewall. The job of this firewall is similar to that of the physical firewall which we know. The job of the physical firewall is to stop the fire from spreading across from one side to the other. Similarly this firewall protects the unwanted elements from entering the system and spreading across the system thus causing damage to the system.