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Configuring IPCop Firewalls by James Eaton-Lee, Barrie Dempster

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The OSI Model

The OSI model is shown in the following figure:

The OSI Model

Layer 1: The Physical Layer

The physical layer encompasses the physical medium on which a network is built. Specifications that operate within the physical layer include physical interfaces such as ports, voltages, pin specifications, cable design, and materials. A network hub is a layer-one device.

Layer 2: The Data Link Layer

The data link layer provides connectivity between hosts on the same network segment. MAC addresses are used at the physical layer to distinguish between different physical network adapters and allow them to communicate. Ethernet is a layer-two standard.

Layer 3: The ...

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