A firewall is a network security system, either hardware or software-based, that controls incoming and outgoing network traffic based on a set of rules.

A firewall physically sits between your network and the Internet and hides your network from others on the Internet.

At its most basic level, a firewall is an Internet router that makes decisions on what to let in and out of your network and what to block. Before firewalls emerged in the late 1980s, the only real form of network security was performed by access control lists (ACLs) residing on routers. ACLs determined which IP addresses were granted or denied access to the network.

Although no technology can guarantee complete safety, a properly designed network with a firewall system, reputable antivirus software, and alert support staff can significantly reduce the risk.

Port-based firewalls are often used as a first line of defense, providing coarse filtering of traffic and segmenting the network into different password-protected zones.

One drawback to port-based firewalls is that they use protocol and port to identify and control what gets in and out of the network.

This port-centric design is ineffective when faced with malware and evasive applications that hop from port to port until they find an open connection to the network. Such firewalls themselves have little ability to identify and control malware.

Solutions that have added anti-malware capabilities to port based firewalls either as a blade module or as a UTM (Unified Threat Management) platform have typically suffered from poor accuracy and severe performance degradation.

Unless defined in the policy, all traffic on a firewall is implicitly denied.

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