How Does a Firewall Work?

In the physical world, a firewall is a partition designed to inhibit or prevent the spread of fire. This physical barrier can greatly minimize the damage caused by the flames. But in the world of computing, how does a firewall work to protect your network?

In computer networking, a firewall is a software program or hardware appliance that is designed to prevent unauthorized access to or from a private network. This network security device monitors incoming and outgoing network traffic and decides whether this traffic needs to stop or go (be allowed or blocked) based on a set of security rules. Think of a firewall as a bouncer at a nightclub — the firewall is located at the entrance to corporate networks, applications, databases and other resources. The firewall (like a bouncer) scrutinizes the incoming (and outgoing) traffic to decide which packets of data get to pass through and which get rejected.

Firewalls are the first line of defense in network security as they establish a barrier between your secured and controlled internal network and untrusted outside networks, such as the internet. A firewall blocks unauthorized access while permitting outward communication. A firewall needs to be able to defend resources, validate access, manage and control network traffic, record and report on events and act as an intermediary.