What Is a Firewall? and types of Firewalls:

Firewalls are often categorized as either network firewalls or host-based firewall. Network firewalls filter traffic between two or more networks and run on network hardware. Host-based firewalls run on host computers and control network traffic in and out of those machines.

Firewalls may also be a component of your computer's operating system. For example - Windows Firewall is a Microsoft Windows application that notifies users of any suspicious activity. The Application can detect and block viruses, worms, and hackers from harmful activity.

Types of Firewalls :

Packet Filter :

Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.

Application Gateway :

Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.

Proxy Server :

It intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.

Circuit-level Gateway :

It applies security mechanisms when a connection is established. Once the connection has been made, packets can flow between the hosts without further checking.

Next Generation Firewall (NGFW) :

Work by filtering network and Internet traffic based upon the applications or traffic types using specific ports. Next Generation Firewalls (NGFWs) blend the features of a standard firewall with quality of service (QoS) functionalities in order to provide smarter and deeper inspection.