What is a Firewall?
Firewall is a piece of software or hardware that monitors unsolicited traffic into your PC. Like a security guard at your home or office, it watches all that happens, and keeps the bad guys out – by looking at the ID of everything that comes into or goes out of your device, which has an IP Address and Port number.
Different types of firewalls use a variety of filtering techniques. The simplest, called packet filters, work at the lowest level of the standardized network model, the OSI (Open Systems Interconnection) layer 3. Packet filters look at individual data packets to see where they came from and where they are going, then decide whether to allow them in, reject them and return them to their original source or for forward them.
The next generation of firewalls, called stateful inspection firewalls, are more sophisticated. They examine data packets to determine what they’re containing, and then match that information with the rules of established policies. This allows a higher degree of accuracy in granting access and supports the protection tools inside the firewall, such as anti-virus programs.
More advanced firewalls, such as those from Cisco Systems, integrate User Identification technology to improve their ability to grant and deny access based on who is requesting it. This is accomplished by linking the firewall with a directory service that stores user IDs and links them to network activities. For example, a school may want to deny students access to its social media server, and the firewall can be configured with a rule that ties this activity to the student’s directory service login and user group membership.