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IP Routing Fundamentals by Mark A. Sportack

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A Closer Look at Routers

A router is an intelligent network device that operates predominantly at the first three layers of the OSI reference model. Routers, like any host, are actually capable of operating at all seven layers of the OSI reference model. Depending on your particular configuration, you may or may not use all seven layers of functionality. However, the need for the first three layers is virtually universal. Communications across the first two layers allows routers to communicate directly with LANs (data link layer constructs). More importantly, routers can identify routes through networks based on Layer 3 addresses. This enables routers to internetwork multiple networks, regardless of how near or far they may be, by using network ...

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