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Firewalls in Network Security: Features & Functions

Instructor: Beth Hendricks

Beth holds a master's degree in integrated marketing communications, and has worked in journalism and marketing throughout her career.

Firewalls operate as a type of fence to protect what's coming into and leaving your network. In this lesson, you'll learn more about their functionality and some features that are common in today's firewalls.

Building Barriers

Alex lives on a small residential street outside of Austin. He has long enjoyed his peaceful neighborhood, where he has knows just about everyone on his block for years. A new family, however, has moved in next door and the small children there frequently end up in his yard. Alex is not a bad neighbor, but he doesn't want the children to encounter his very large dog.

He decides to have a fence put up around the perimeter of his yard to protect the children next door and to help keep his dog inside.

So, maybe you read the title of this lesson and you're asking yourself, ''What does a fence have to do with computers and firewalls?'' Actually, a lot!

Think about a firewall as a type of digital fence you can put up on your computer or network to protect it from malicious content or unauthorized access. Firewalls act as a type of filter in network security, allowing or disallowing incoming or outgoing activity based on security measures you specify. They are either hardware or software based, meaning that either a physical device or a software program is used to provide security for your system.

Firewall Functions

Firewalls perform two basic security functions for a network. These are known as packet filtering and acting as an application proxy.

Packet Filtering

In packet filtering, sometimes called static filtering, the firewall operates at the packet level. What this means is that the firewall looks at each data packet as it comes to, or leaves, the computer network. While it's examining these packets, it uses user-defined rules to determine whether to accept or reject the packet. In this way, packet filtering is a type of gatekeeper that determines what can pass through, thanks to system monitoring and the network's rules.

For example, Lisa's company may use packet filtering to permit packets to travel back and forth in your email server, while disallowing any other packets that try to enter or leave your network. Unbeknownst to Lisa and her colleagues, packet filtering is working behind the scenes by checking out the data packet's information based on its originating and destination addresses, what protocol is being used and port data.

Application Proxy

The other function of a firewall is to act as an application proxy. Often referred to as an application level gateway, this firewall lives at the application level rather than the packet level. Packet filtering, for example, cannot recognize malware trying to break into your system because it doesn't have any basis for understanding the entire application. A firewall acting as an application proxy can actually stop information between your internal network and the network outside your walls because it understands the application being used.

For example, a cybercriminal overseas is trying to target Lisa's company by sending emails containing malicious attachments he hopes the employees will download to their devices. Using a firewall that acts as an application proxy, the system is able to recognize and block the malware attempts because it can examine the entire application being used. Most computer experts agree that this type of firewall protection is more thorough and robust than packet filtering alone.

Now, let's take a look at some of the various features firewalls can have.

Firewall Features

If you've ever tried to access a social media website from your work computer and been unable to log on, your company's IT department may be to blame. The ability to block social networking sites (or any other website, for that matter) is just one of many features that firewalls can provide.

Here are some other common ones:

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