Overview On Firewalls In Linux Operating Systems Computer Science Essay

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This project report discusses the security mechanisms in context with the Linux operating system, the focus being the Firewall security. Moreover there are also other security mechanisms such as Host security, Cryptography, Server security and Network security. Security is a very important aspect when it comes to information technology especially network security. Rushmore (2010) mentions that the server security can be monitored accordingly by taking care of the passwords, file transfer and remote logins.


A firewall refers to a combination of gateway and a proxy which act as network server functions. A Gateway is a path whereby a connection between two computers can be made, one computer has to establish a connection and the other has to allow access. A proxy on the other hand is useful when two computers on the same network want to communicate and share files, the two computers will communicate through a proxy server. A firewall can protect against viruses, worms and other harmful applications from the internet. The complexity of the firewall depends upon the network traffic it’s exposed to. The types of Linux firewalls include the Filtering firewalls and Proxy servers. There is also the IP Tables firewall which is used by a number of Linux operating systems including Debian, Ubuntu and the Red Hat Linux.


The main objectives of this project report are:

To explain what a firewall is and what it does

To evaluate the types of firewall in context with the Linux Operating System

To discuss the IP Tables Linux firewall


From way back ipchains was the most used Linux firewall. With change in time and technology the Net filter organization modified the ipchains with some features and named it iptables. The modifications include better speed and reliability, the firewall can now monitor the connection through it and also the network address translation has been improved. There is also a feature that that helps to block the Dos attack (Denial of Services). The iptables now has taken over in Red Hat and Fedora Linux and it is installed as a default firewall as it is considered to be fast and secure (Bautts et al. 2005).



A Linux firewall is used for a couple of reasons as long as it is security related. Different Linux operating systems use different types of firewalls but some uses the same type. The Red Hat Linux, Debian and Ubuntu use the IP Tables Firewall. Some of the reasons why people use a firewall are:


LHN (2010) states that unauthorized access is when a certain network is used by people who do not have privileges to use it. People who have unauthorized access can end up obtaining high classified information which should not be seen by other people. To prevent this from happening, a Linux firewall can be installed and be configured to only allow certain users and not everyone.


Spoofing is whereby a user pretends to be the other in the network by forging an IP address. A firewall can also be installed to help overcome this. A proxy server can be established and every time a user wants to access the internet, he/she will have to enter the proxy combinations (LHN 2010).

Moreover, Stone (2004) adds on and mentions that a Linux firewall can be used to block some sites to certain users. For example, a school may block all the music sites so that the students cannot be able to access them and focus more on their school work. Also a firewall can be useful to prevent attack by worms, viruses, Trojans and other harmful applications.


There are two types of firewalls involved with Linux operating system. They include filtering Firewalls and proxy servers which are also known as firewalls. However there is also the IP Tables firewall.


This kind of firewall is built into the Linux kernel and its use is to block selected network packets. This firewall uses the IP packet structure because filtering packets is more like a router. The person using the network needs to put only the IP number to get access rather than passwords. However, this can cause a problem if later a user wants to use the Dynamic IP assignments because new IP numbers will have to be used (Grennan 2000).


According to Grennan (2000), Proxy servers are the ones which make the network connections available. Moreover there are two types of proxy servers namely the Application and the SOCKS proxies. An example of an application proxy is whereby two users share files, the client will send the proxy servers in order for a connection to be established but however login may be required. Moreover the SOCKS proxy is just for establishing a connection outside. Authentication is not required.


As mentioned above, the IP Tables is used by a number of Linux Operating systems as it is considered to be fast and secure. It was modified from IP Chains, the difference is the newly features installed. The IP Tables can be started by using some commands, also commands can be used to restart and stop the IP Tables (LeBlanc 2005)

The IP tables consists of three tables namely the mangle, the filter queue and the Nat queue table. The mangle table is used to find or monitor the service quality in the TCP header, the filter queue on the other hand is responsible for filtering packets and to do so it has three chains for putting firewall policies. Lastly is the Nat queue which addresses network translation, it has two chains to complete this task (LHN 2010).


A firewall refers to a combination of gateway and a proxy which act as network server functions. Certain Linux operating systems use different firewall like the IP tables firewall to protect against unauthorized access, worms and viruses. The Red Hat Linux, Ubuntu and Debian uses the IP tables firewall as their default firewall the reason being that it is considered to be fast and secure. Moreover there is also the filtering and the proxy server firewalls, the filtering firewall is built into the Linux kernel and its use is to block selected network packets. Proxy servers are the ones which make the network connections available. Firewalls are very important when using a computer especially in a business environment to control the access of users into the server or system.