Honestly, I’ve been hearing firewalls a lot of time but I don’t know personally firewalls are for up until I have to learn firewall because of this exam. After the discussion, i made researches and figure out the importance and the purpose of firewall in a network.
Purpose: allow or deny traffic flow in and out of a network based on pre-defined security information. Firewall acts as a bouncer in a night club that selects or denies who is allowed to enter. If there will be an exemption, the bouncer should look at the VIP list to check who is allowed to enter the night club. Let us try to examine the picture below:
First, let me discuss the parts of the figure: inside zone is the LAN and of course the zone which is most trusted by default, the outside zone is the least secured zone and the DMZ zone is the mediocre among all. Let us discuss also the security level on each zones, the least security level means the least secure the zone is and since the relationship is directly proportional, we can say that the higher the security level, the more secure the zone is.
Inside zone can:
access outside zone and DMZ zone
DMZ Zone can:
access outside zone
but cannot access inside zone because inside zone has higher security level to it
Outside zone can:
has no access at both zones because it has the least security
“For every rule, there is an exemption.”
Likewise I told you that firewall acts as bouncer that follows the protocol but also provides exemption to those listed on the VIP lists, VIP list that I am referring since before are the ACCESS-LIST.
Access-list is a way to override the established security protocol by the firewall. Let say that you are in the inside zone and since you have full access to the outside zone let’s say the internet to access facebook and it is not allowed in the office, the network admin may block facebook in the access-list so that no one in the inside zone can access facebook.