00:00What is a firewall? Now a firewall is a system that is designed to prevent
00:05unauthorized access from entering a private network by filtering the
00:10information that comes in from the internet. A firewall blocks unwanted
00:15traffic and permits wanted traffic. So a firewall's purpose is to create a safety
00:20barrier between a private network and the public internet. Because out on the
00:26internet there's always going to be hackers and malicious traffic that may
00:30try to penetrate into a private network to cause harm. And a firewall is the main
00:35component on the network to prevent this. And a firewall is especially important
00:40to a large organization that has a lot of computers and servers in them. Because
00:45you don't want all those devices accessible to everyone on the internet
00:50where a hacker can come in and totally disrupt that organization. So that's why
00:55you need a firewall to protect them. So a firewall that's used in computer
01:00networks is very similar to how a firewall works in a building structure. In fact
01:05that is where the word firewall came from. A firewall in a building structure
01:10provides a barrier so that in the event of an actual fire on either side of the
01:15building, the firewall is there to keep the fire contained and to keep it from
01:20spreading over to the other side. So the firewall is there to keep the fire from
01:24destroying the entire building. But if the firewall wasn't here the fire would spread
01:30over to the other side and then the whole building would be destroyed. And a
01:34network firewall works in a similar way as a structure firewall. It stops harmful
01:39activity before it can spread into the other side of the firewall and cause harm
01:45to a private network. So in today's high-tech world a firewall is essential to
01:50every home and especially in the business or an organization to keep their network
01:55safe. Now a firewall works by filtering the incoming network data and determines
02:00by its rules if it's allowed to enter a network. And these rules are also known as
02:05an access control list. These rules are customizable and are determined by the
02:11network administrator. The administrator decides not only what can enter a network
02:16but also what can leave a network. So these rules either allows or denies permission.
02:23So as an example here we have some rules in a firewalls access control list and it
02:28shows a list of IP addresses that have been allowed or denied by this firewall.
02:34And as you can see traffic from some IP addresses are allowed to enter this
02:38network but traffic from one IP address has been denied. So if traffic from this IP
02:44address tried to get into this network the firewall will deny it because of the
02:49rules that are set in the firewall. But the other IP addresses are granted access
02:54because the rules allow them. Now firewalls don't just make rules based on IP
02:59addresses but they can also make rules based on domain names, protocols, programs,
03:05ports, and keywords. So let's say in this example the firewall rules are
03:10controlling access by port numbers. And let's say that the rules have allowed
03:15incoming data that's using port number 80, 25, and 110 and the data using those
03:21ports have been given access to this network. So any incoming data that's using
03:26those ports can pass through the firewall. But also in this firewall the rules have
03:32denied any data that's using port numbers 23 and 3389. So any incoming data that's using
03:39those port numbers the firewall will deny access and it won't get past the firewall.
03:44So in a nutshell this is how firewalls basically work. Now firewalls do come in
03:50different types and one type is called a host-based firewall and this is a software firewall.
03:56This is the kind of firewall that is installed on a computer and it protects that computer
04:01only and nothing else. So for example later versions of Microsoft operating systems come
04:07pre-packaged with a host-based firewall. And you can see that example here. And there
04:12are also third-party host-based firewalls that can be purchased and installed on a computer. So
04:18for example Zone Alarm which is a popular third-party host-based firewall. And also a lot
04:25of antivirus programs will have a built-in host-based firewall. And another type of firewall is
04:32called a network-based firewall. A network-based firewall is a combination of hardware and software.
04:38And it operates at the network layer. And it is placed between a private network and the public
04:44internet. But unlike a host-based firewall where it only protects that computer, a network-based
04:51firewall protects the entire network. And it does this through management rules that are applied to
04:57the entire network so that any harmful activity can be stopped before it reaches the computers. Now
05:04network-based firewalls can be a standalone product which is mainly used by large organizations. And
05:11they can also be as a built-in component of a router which is what a lot of smaller organizations
05:16rely on. Or they can also be deployed in a service providers cloud infrastructure. Now a lot of
05:24organizations will use both network-based and host-based firewalls. They will use a network-based
05:30firewall to protect the entire network as a whole. And they will also use host-based firewalls for their
05:37individual protection for their computers and servers. And by doing this, it'll ensure maximum
05:43protection. Because if harmful data just so happens to get past the network firewall, the host-based
05:49firewalls on each computer will be there to stop it. So thank you everyone for watching this video on
05:57firewalls. Please subscribe and I'll see you in the next video. Thank you.
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