What is a Firewall in Network Security? - Role & Use

Instructor: Luis Cruz

Luis is an IT executive with over 18 years of experience and has a master's degree in Management Information Systems.

The network firewall is an important piece of equipment that protects your network from hackers and other cyber criminals. Its use is essential if your business is connected to the Internet, and it's highly recommended for residential users too.

What's a Firewall and How Does It Protect You?

Imagine you just moved in to one of those fancy apartments in New York City (NYC). For security, the apartment building has a doorman to control who comes into the building. You like the idea of the doorman! He makes you feel safe in your new place of residence.

Much like a doorman controls who comes into the building and can keep a bad crowd out of your apartment, a network firewall also controls what comes into your network. However, one key difference in this analogy is that while your friendly doorman won't ever prohibit you from leaving the apartment, a firewall may often do just that; controlling both what comes in and what goes out of your network.

Imagine you moved into a building with a doorman
NYC Buildings

How Traditional Firewalls Work

The firewall controls connections coming into your network so that only the connections that are allowed can get through. Much like the doorman will know all the residents and have a list of authorized guests, a firewall has something called an access policy.

An access policy is simply a set of rules that determine who gets in or out of your network and who doesn't. Firewall access policies are created by firewall administrators, who are IT experts that know and understand how to setup the firewall to protect your network.

Firewalls are also used to segment your network into places called zones. Zones are smaller chunks of your network that share similar attributes. Going back to our fancy apartment analogy, the doorman knows that residents go to the elevators, employees go to the door on the right, guests go to the registration desk to check in, and the bad crowd stays out.

The doorman would immediately stop a guest who tried to go to the door on the right, that's only for employees! In essence, your apartment building is segmented into four zones; the resident zone, the employee zone, the guest zone, and the outside zone, where swarms of the bad crowd are trying endlessly to get into your fancy apartment.

Firewall and Doorman Analogy
Firewall Doorman Analogy

Similarly a firewall protects your network. It directs and controls traffic on your network using various access policies that may apply to the various zones. Firewalls can potentially have many zones associated with them. Simple networks might have between two and four zones. More complex networks can have hundreds of zones.

Firewall Example
Firewall Example

The Evolution of the Firewall

Can it all be that simple? The bad crowd is getting smarter and more cunning, learning new ways to trick the doorman so that they can get into your comfy building. Perhaps, one will dress as a delivery man and approach the doorman indicating that he has a package to deliver. Another might steal or falsify an employee ID badge in hopes of making his way to the door on the right, uncontested.

Unfortunately, this is true of the cyber-world as well. Cyber criminals, or hackers, are coming up with new tricks almost daily to try to bypass the security and protection a firewall offers. Of equal importance is the insider threat. What if some of the bad crowd pulled their money together and bought an apartment in your fancy building? Then the one who gets in puts all his bad crowd friends on the guest list.

As these types of scenarios develop in network security, firewall makers are designing smarter and more adaptable firewalls. In today's marketing buzz-word terminology, these are known as next-generation firewalls. Think of it as giving your doorman a sixth sense that would help him identify and stop the bad crowd that use costumes, fake IDs, guest list corruption, or any other type of trickery to get in.

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