Firewalls are used to prevent unauthorized Internet users from accessing private networks connected to the Internet. All data entering or leaving the intranet pass through the firewall, which examines each packet and blocks those that do not meet the specified security criteria.

Firewalls examine all the data packets passing through them to see if they meet the rules defined by the ACL (Access Control List) made by the administrator of the network. Only if the Data Packets are allowed as per ACL, they will be transmitted over the Connection.

Firewalls are configured to protect against unauthenticated interactive logins from the outside world. This helps prevent hackers from logging into machines on your network. Firewalls are essential since they provide a single block point, where security and auditing can be imposed.

The purpose of the Firewall is to protect a private network from the threats of hackers coming from the Internet (a public network).

Firewall can filter contents on the basis of Address, Protocols, Packet attributes, State, and it’s generally only Screen the Packet headers.