What is a firewall?
In network security, firewall is considered a first line of defense in protecting private information. "A firewall sits at the junction point, or gateway, between the two networks, which are often a private network and a public network such as the Internet." (John V. Harrison, Hal Berghel, 2004, A Protocol Layer Survey of Network Security). It is a system designed to prevent certain access to or from another network. It has two mechanisms and they are blocking or permitting accesses.
Why do I need a firewall?
Nowadays, computers and internet become more and more popular, companies and people will save their sensitive data or their little secrets which they want to protect on their computers. However, internet is not a safe place; there are people who like to steal data from others or just enjoy ruining other people's day by destroying others' computer systems. And, firewall is used to protect you from those bad people and still letting you to get your job done.
"The primary purpose of the ... firewall is to take a proactive and preventive measure approach to mitigating the numerous electronic security intrusions possible in today's Internet age." (University of Cincinnati, 2005, Self Help). "Firewalls then provide the next level of protection by denying access to certain network services and ports based on policy and need." (Eugene H. Spafford, 2003, Cyber Terrorism: The New Asymmetric Threat). As we all know, a company is rarely to have only a gate security to check a person who try to enter and without receptionist or other securities to check that person on the way in, if it is reasonable to have layers of security in the company, it is also reasonable to have layers of security on our network. "Some firewalls can also...