What Are Computer Firewalls?

A firewall is usually the first line of defense when it comes to protecting private information and keeping out threats like viruses and malware. Firewalls monitor incoming and outgoing traffic on a computer network—whether it’s your home Wi-Fi network or a large shared network at a company.

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What Does a Firewall Do?

Firewalls work as a barrier between your protected network and unauthorized users and networks. But a firewall isn’t foolproof—it may act as a bouncer that checks out individual users before they’re allowed behind the velvet rope, but it may not catch every fake ID, and it won’t hunt down and kick out the riff raff if they do sneak by. That means you shouldn’t rely on a firewall alone to keep the bad element out of your network, files, and info.

How Do Firewalls Work?

You can implement firewalls in either software or hardware form, or as a combo. Once you have a firewall in place, all traffic entering or leaving the protected network must pass through it. The firewall inspects each message or action against specified security criteria. Anything that isn’t up to snuff gets blocked.

Types of Firewalls

There are four main types of firewalls. Although each is designed to perform the same basic security function, the way they do their job is different. Many firewalls combine two or more of these types to deliver an extra security punch.

Packet Filters 

This type of firewall looks at information known as packets. Packets are messages that consist of control information and user data. Packet filters check each packet of information as a whole instead of examining the specific data. Based on the security parameters, the firewall will allow, drop, or reject the packet.

Application-Level Gateways

These firewalls apply security measures to specific applications and protocols, such as File Transfer Protocol (FTP) or Hypertext Transfer Protocol (HTTP). Application firewalls may intercept all packets entering or leaving a specific application, which adds extra security but can also slow down the transfer of data.

Circuit-Level Gateways

A circuit-level gateway controls how information is transmitted over a single network. Once this type of connection is made, packets can pass over the network between designated hosts without any additional review. This prevents the latency issues that application-level gateways can face.

Proxy Servers 

A proxy server is a firewall that hides the network address of the computers on the network. This means the proxy server connects with the internet and handles all communication, protecting the computers and the network behind it. You can set up a proxy server to allow or block everything from certain types of traffic (for example, web pages or HTTP files). Because a proxy server intercepts and analyzes all traffic passing through, it can slow down the entire network.

Firewalls are crucial to any internet security plan. Consider using a firewall in conjunction with other security measures like antivirus software and identity theft protection.


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Rebecca Edwards
Written by
Rebecca Edwards
Rebecca is the lead safety reporter and in-house expert for SafeWise.com. She has been a journalist and blogger for over 25 years, with a focus on home and community safety for the past eight. Rebecca spends dozens of hours every month poring over crime reports and spotting trends. Her safety expertise is sought after by publications, broadcast journalists, non-profit organizations, podcasts, and more. You can find her expert advice and analysis in places like TechCrunch, The Washington Post, The Chicago Tribune, The Miami Herald, NPR, HGTV, MSN, Reader's Digest, Real Simple, and an ever-growing library of radio and TV clips.

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