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CCNA® Cisco Certified Network Associate: Study Guide, Seventh Edition by Todd Lammle

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TCP/IP and the DoD Model

The DoD model is basically a condensed version of the OSI model—it’s composed of four, instead of seven, layers:

  • Process/Application layer
  • Host-to-Host layer
  • Internet layer
  • Network Access layer

Figure 3-1 shows a comparison of the DoD model and the OSI reference model. As you can see, the two are similar in concept, but each has a different number of layers with different names.

note.eps

When the different protocols in the IP stack are discussed, the layers of the OSI and DoD models are interchangeable. In other words, the Internet layer and the Network layer describe the same thing, as do the Host-to-Host layer and the Transport ...

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