On the sixth day of A2Z Challenge 2019, I shall touch the A2Z of Firewall. In this post, I will tell you about the basics of Firewall. In real life, a physical firewall is made of inflammable material that prevents the spread of fire in an establishment. Similarly, in Computer Science, a firewall acts as a barrier (filter) between a trusted internal network (LAN) and an untrusted external network (Internet).

You can set up a firewall in two ways:

1. Using Software: Most of the Antivirus software comes with a built-in firewall.
2. Using Hardware: You can set up a server computer to acts as a firewall.

You should always place the firewall between your trusted network and untrusted network. You can configure a firewall in various ways:

1. By allowing traffic from all IP addresses except blacklisted IPs.
2. By allowing traffic only from a few IP addresses that are whitelisted.

A2Z of Firewall – Types of Firewall

There are two categories of firewall – network firewall and host-based firewall. Network firewalls filter traffic between two networks. Host-based firewalls run on host computers and control their incoming and outgoing traffic.

There are three types of firewall:

• Packet Filters:  A packet is the unit of data that which is transmitted through the Internet. Packet Filter firewall allow or block the packets based on a few criteria such as source IP address, destination IP address etc. Packet filters can be further divided into 2 sub cateogories – stateful and stateless.
  • Stateless: Stateless packet filter firewalls aren’t aware of the of data transmission path. So, they check each and every packet in isolation.
  • Stateful: Statelful packet filter firewalls can track the state of packets. They are aware of the data transmission path. This type of firewall is better in detecting unauthorised access.
• Application Firewall: Application Firewall monitors the packets that are sent to and from an application.

In this post, I have touched the A2Z of Firewall (in basics). Have any questions? Feel free to ask them in the comments section!