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Information Security The Complete Reference, Second Edition by Mark Rhodes-Ousley

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CHAPTER
15 Firewalls
 
Firewalls have been one of the most popular and important tools used to secure networks since the early days of interconnected computers. The basic function of a firewall is to screen network traffic for the purposes of preventing unauthorized access between computer networks.
What generates that traffic? Applications. Running internally and externally on servers and workstations (and sometimes on other network devices or appliances), applications are the purpose of all network traffic. Thus, what we’re really talking about when we’re discussing firewalls is application communication management on layers one through seven of the OSI stack (which is described in Chapter 14). Applications are what firewalls are ...

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