Published at LXer:

A packet filtering firewall, designed to regulate incoming and outgoing packets from a network or an operating system, is akin to security personnel guarding the entrance to a commercial or residential property. Such a system has very little authority, unless given additional powers, in what applications inside the operating system or network are able to do. That is where an application “firewall” comes into play. It is designed to ensure that applications in an operating system (or in some instances, a network) adhere to access control rules that govern their “activities.”

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