Network Security Essays

15363 Words Jan 9th, 2015 62 Pages
CHAPTER

Firewall Fundamentals

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o some network administrators, a firewall is the key component of their infrastructure’s security. To others, a firewall is a hassle and a barrier to accomplishing essential tasks. In most cases, the negative view of firewalls stems from a basic misunderstanding of the nature of firewalls and how they work. This chapter will help dispel this confusion. This chapter clearly defines the fundamentals of firewalls. These include what a firewall is, what a firewall does, how it performs these tasks, why firewalls are necessary, the various firewall types, and filtering mechanisms. Once you understand these fundamentals of firewalls, you will be able to look beyond the unschooled opinions, common
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A firewall is like a border sentry. A firewall is like a gateway and is often called a “security gateway.” A firewall is like a traffic control device. A firewall is a filtering device that enforces network security policy and protects the network against external attacks. A packet is a unit of information that is routed between one point and another over the Internet or any other network. The packet header includes information such as source, type, size, and origin and destination address. As a filtering device, a firewall watches for traffic that fails to comply with the rules defined by the firewall administrator. Firewalls can focus on the packet header, the packet payload (the essential data of the packet) or both; or on the content of a session, the establishment of a circuit, and possibly other assets. Most firewalls focus on only one of these. The most common filtering focus is on the header of the packet, with the payload of a packet a close second. Filtering allows what you want on your network and denies what you do not. Filtering relies on filtering rules. Each rule has a pattern of concern and a response the firewall will make if an incoming element matches the pattern. Firewalls follow a philosophy or stance of security known as deny

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