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Eleventh Hour Security+ by Ido Dubrawsky

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Firewalls

A firewall is the most common device used to protect an internal network from outside intruders. When properly configured, a firewall blocks access to an internal network from the outside, and blocks users of the internal network from accessing potentially dangerous external networks or ports.

There are three firewall technologies examined in the Security+ exam.

  • Packet filtering works at the network layer of the Open Systems Interconnect (OSI) model and is designed to operate rapidly by either allowing or denying packets.
  • Application-layer gateways operate at the application layer of the OSI model, analyzing each packet and verifying that it contains the correct type of data for the specific application it is attempting to communicate ...

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