# Firewall

Firewall can either be software or hardware.

It is a system that is designed to prevent unauthorized access from entering a private network by private network by filtering the information that comes in from the internet.

It blocks the unwanted traffic and permits wanted traffic.

It filters the incoming network data packets and determines by its access rules if it is allowed to enter the network.

It is essential to keep business or network safe.

One way that a firewall controls the flow of traffic coming into and out of a network is through its access control list (ACL).

ACL is the list of rules on what can access the network.

It either allows or denies the permission.

Some ip address would be allowed and some would be blocked.

Implicit Deny-

Most firewalls come with a default rule of implicit deny.

The firewall will only allow the traffic to network that the ACL specifically says that it will allow.

For ex- Port 80 is allowed then you will be allowed to access contents of port 80 only.

You won’t be able to access other things.

To access those(blocked) services is you have to specifically allow them by granting them access in ACL.
