A2Z 2019 – Day 6 : ‘F’ – Firewall

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!




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  1. Another informative post!

  2. Useful info!!

  3. An informative post! loved it

  4. Very insightful! Your post improved my knowledge about Firewall.

  5. Another insightful post

  6. Short and sweet, but very informative.

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