The term “Firewall” comes from an incident when people are protected from fire. It acts as the shield and protects the people from fire.

A firewall is used in the computer network security system that monitors the incoming and outgoing network traffic based on security rules. And it is able to control the network traffic. A firewall acts as a barrier to protect a website from unsecured resources.

A firewall has a set of rules and it determines the network traffic whether to allow or block a connection. For the security purpose, some organization implements this to protect from the network attacks and more different types of security threads. It blocks the unauthorised access from another network. There are many types of firewall. The firewalls that are cheaper provides a low-level security. It depends on your requirement and the security level needs to protect the network of your personal or for your organisation.

The most arrangement involves a number of separate machines and is known as a perimeter network. Firewall is categorised into network firewall or host-based firewalls. The less security level firewall may encounter the security that has a breach and more attacks.

What is Firewall

Firewall is the vital piece of internet/network security. To prevent unauthorised internet user or hacker to access networks which are connected to the Internet. The firewall monitors the incoming and outgoing network packets allow the legitimate one to access the network. It illustrates like the boundary or a wall to keep the network in the secure zone. The firewall is categorised as the network firewalls or host-based firewall. The firewall has separate rules and it follows to allow access for the particular packets in the network.

Categories of Firewall:

Hardware firewalls:

Hardware is a stand-alone product and recently firewalls are typically found in broadband routers, and it is considered as the important part of computer and network setup. And it protects the local computer while using the broadband internet connections. A hardware firewall uses the packet filtering to examine the header of a packet to determine its source and destination. The firewall checks with the set of rules and it decides whether to allow or reject a network.

Software firewalls:

For the home users, the software firewall is recommended to secure their computer. The software firewall is installed in the system as the system application software. It protects from the security thread as same like the hardware firewall. It protects the control or gains access to your computer. From most common issues, the Trojan program or e-mail worms and etc. can be protected by the software firewall. It blocks the unsafe applications and malicious application and virus file execution on the local machine and it protects our system like the anti-virus software application. It looks on the network setup to protect the request and response from the local machine to the server and vice versa process also.
The difference between a software and hardware firewall are more, and it is the best solution for computer and network to protect your system. Keep on updating your software firewall and operating system which are being used in your home or organisations to maintain an optimum protection. And test whether the network connection and firewall settings are configured correctly.

Types of Firewall

1. Packet-filtering Firewalls
2. Stateful inspection firewall.
3. Application-level firewall.
4. Multilayer inspection firewall.
5. Proxies
6. NAT – Network Address Translation.

Note: Payloads are not visible to the Packet filtering firewall.

Configuring a firewall:

To build the Linux IP firewalls, it is necessary to have a kernel built with IP firewall support and the appropriate configuration utility. The 2.2x kernel marked the release of the third generation of IP firewall for the Linux called IP chains.

The IP chains program is similar to the ipfwadm. Later in the fourth generation Linux kernel IP firewall is called as Netfilter. Then newly it referred as iptables.

The Linux kernel provides various types of built-in features that function as the IP firewall. It includes a number of IP filtering methods in different ways and provides the mechanism to a configuration. The Linux kernel must support the IP firewalling configuration. Select the appropriate configuration while creating a menuconfig of your kernel.



ipfwadm stands for the (IP Firewall Administration). It is the tool used to build the firewall rules for all the kernels prior to 2.2.0. Its commands have some syntax to be followed and it is very confusing and complicated. There may be specific software package for that you have to install. You can obtain the packages from the in the /pub/linux/ipfwadm directory and compile it.


The ipchains can somewhat look like a puzzle and frustrate to use for the first time. But it provides all the flexibility of ipfwadm with simplified command syntax. In additionally, it provides the chaining mechanism that allows you to manage multiple rulesets and link them together also.


It is quite similar to the ipchains syntax. The changes are improved and as a result, the tool is being redesigned to be extensible through the shared libraries.

Software Firewalls

To disable or Turn off Linux Firewall, open the terminal in your Linux operating system. (Red hat/Cent OS/ Fedora). Login as a root user in the Linux system. Here an example is shown for the iptables utility.


To disable the service:

#/etc/init.d/iptables save
# /etc/init.d/iptables stop

To turn off firewall boot:

# chkconfig iptable off

To enable the service:

# /etc/init.d/iptable start

To run a firewall on boot:

# chkconfig iptables on

Advantages of Firewall:

1. Prevents from the attacks like

a. IP Spoofing Attacks
b. Sniffer Attacks
c. Man in the Middle Attack

Dis-advantages 0f Firewall:

1. Packet filters do not understand application layer protocols.

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