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Cisco Firewall Technology by Andrew Mason

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Section 1 - Firewall Technologies

What Is a Firewall?

Networks today are seldom islands. With the massive uptake of the Internet, most organizations now have single or even multiple connections to external networks. For example, I have seen companies with Internet connections for general browsing and mail services, Internet connections for virtual private network (VPN) services, and connections that form extranets with third-party businesses. These connections (combined with inter-site communications for both data and voice), sometimes over public and sometimes over private networks, make identifying where the edge of their network (also called the perimeter) exists problematic.

The mention of a network perimeter leads us to an important topic: ...

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