A Firewall Software - Essay Example

A firewall is a device (it could be a software or hardware system) that disallows any illegitimate access towards or from a network. (Davis et al., 2011, p. xx-xx) Firewalls can be employed in either software or hardware or by combining both of them. Today firewalls are mostly configured to stop unauthorized access from the internet to the private local area networks (LANs) connected with the internet. Firewalls are configured to monitor all the data that enters or leaves the Intranet. It examines every packet and drops those that do not fulfill security standards set by network security engineers.
The followings are the advantages and disadvantages of using a firewall.
Advantages
• Firewalls track the suspected packets and drop them before accessing the network.
• Firewalls prevent hostile intrusion from the internet to the private local area networks (LANs).
• Firewalls are configured to permit access to users on specific services over the internet.
• A hardware firewall manages the number of systems simultaneously in the network while a software firewall can do the same for an individual computer.
• Firewalls can hide the DNS information of all internal hosts
• A firewall allows a method to implement the network security policy standards of an organization
• Firewalls are configured to decide the direction of particular service requests and are permitted to flow
• Manages the use of particular services are used (e.g. filtering of e-mail)
Disadvantages
• Use of software firewall degrades the performance of the system.
• Hardware firewalls are expensive.
• Proper configuration and maintenance of a hardware firewall is not an easy task.
• A hardware firewall sometimes generates false security alarms that encourage the users not to configure security at the system level.
• If a firewall fails to secure the network from intrusion either by no proper configuration or hardware failure, could result in a disaster.
• Firewalls cannot stop malware.
• Still cannot do anything to an insider attack.
Types of Firewall
There are four types of firewalls.
1. Packet Filtering Firewalls.
2. Application Level Firewalls.
3. Circuit Level Firewalls.
4. Stateful Inspection Firewalls.
Packet Filtering Firewall:
A packet filtering firewall is one of the basic firewalls that work on the transport and network layer of the TCP/IP layering model. (In Vacca, 2014, p. 152-153)A packet-filtering firewall monitors packets that are coming in or going out of the network. It accepts or rejects packets based on criteria defined during its configuration. Filtering packets is pretty effective and transparent to users. One main disadvantage of packet filtering is that it is hard to configure.
A packet filtering firewall inspects the header of every packet on all or any of the following.
1. IP address of the source. A thick check should be made essential as most of the time IP spoofers change the source IP to show the source of the packet from somewhere else, instead of showing the source.
2. IP address of the destination. The firewall should be configured to check the IP address instead of DNS names to prevent the misuse of DNS servers.
3. Protocol used.
4. a Port number of TCP/UDP.
5. Message type of ICMP.
6. Fragmentation flags.
7. Settings of IP Options.

Based on the above checks firewall decides the future of the packet either to allow it (ACCEPT) or disallow it (DROP).
Application Level Firewalls:
Application level firewall is generally an application-specific firewall. It is configured with a set of application-specific rules that can give control over the network traffic at the user’s level. (Kizza, 2014, p. 134-135) The main functionality of the application layer firewall is to manage internet browsing, filter emails, and attachment, and transferring of files. Traffic coming inside the network or going outside the network can be denied or allowed based on the different sets of rules. These rules can be one of the following.
• Disallowing attachments in the email system.
• Transferring a custom block page
• Blocking of a custom email reply.
• HTTP request redirection
• Sending a custom FTP reply over an FTP control channel
Circuit Level Firewalls:
A circuit-level firewall is also known as a transparent proxy firewall. These firewalls work at the transport layer, which enables them to collect, monitor, or block every packet in a TCP/ UDP connection. Circuit-level firewall monitors the TCP handshaking between the packets to conclude the legitimacy of the session. Network traffic is filtered based on session-specified rules, for instance when a session is started by the trusted host. Read More