A: TCP/IP Model Lingo

By certskills October 4, 2018 09:05

TCP/IP Model? Check. TCP/IP Models? Yes, two of them, but it’s no big deal. Just take the extra minute to remember the details. The latest practice question asks a question that requires you to recall the differences, with the answers listed here.

The Answers:

A, B


Background: OSI and TCP/IP Models

First, let me comment a moment about the relative unimportance of OSI and TCP/IP models. Although Cisco includes these models in the CCENT and CCNA certifications, any knowledge beyond the basics has almost no practical use today. However, you should recall the models, their layer names, and remember the main features of the lower layers in the models. Also, I think it is useful to remember the small differences between the two versions of the TCP/IP model – hence my choice to offer this question.

As for the two TCP/IP models, RFC 1122 defines one model, with four layers, as seen in the center of Figure 1. Over time, people began preferring an informal version of the model that morphed two items:

  • The former Link layer morphed into two layers (Data Link and Physical) to match the OSI models’ lower layers.
  • The former Internetwork layer changed names to the Network layer to match the OSI model’s naming.


Figure 1: Correlations Between OSI and Two TCP/IP Models


Why the Right Answers are Right

A brief look at the figure shows that two of the answers – Application and Transport – appear to be correct. The names match in both the four-layer and five-layer models, and as implied by the figure. Both models also define the same functions at each of those layers, respectively.


Why the Wrong Answers are Wrong

The answer about the Network layer is incorrect only because of the different name. The Internet (four-layer) and Network (five-layer) layers define the same actions, just with a different name for the layer.

The change to a five-layer TCP/IP model broke the larger bottom layer (Link) into two layers, each with a name to match the OSI models’ terms. Those facts make the answers about the Data Link and Physical layer incorrect because the four-layer model has no directly matching layer by the same name.

Q: TCP/IP Model Lingo
Q: TCP Transport Ports
By certskills October 4, 2018 09:05
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  1. Carl D C May 7, 12:14

    In other study materials that I use the TCP/IP model uses Application, Transport, Internet, and Network Access as another variant of the TCP/IP model. Is this info correct?

    Reply to this comment
    • certskills Author May 7, 14:27

      Yep. The model per RFC 1122 (original model spec) is 4 layers. However, the 4-layer TCP/IP model’s lowest layer has been called, over the years: Link, Network Interface, and Network Access. Then the commonly-used model morphed the lowest of the 4 layers into Data Link and Physical.

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  2. ALEXANDER JOHN UNG July 20, 19:22

    My Cisco Text told me to go to this link. I like the information and the formate it is in. This is like the dessert…..The Cisco Text is the main course of the meal. Thank you!! I will definitely use this as a study aid. ~ Alex Ung (Candidate for the CCENT)

    Reply to this comment
  3. Stephen Gordon March 1, 08:39

    Premium edition e-book
    Figure 1-14 is missing the four-layer TCP/IP model

    Reply to this comment
  4. Chris Dedman-Rollet June 18, 15:58

    Application, Transport, Network,Data Link and Physical are the Modern Model right?

    Reply to this comment
  5. Gus June 27, 20:34

    This is so GREAT to have the chance to review OSI and the TCP/IP models here again. Thank you, Wendell!

    Reply to this comment
  6. David Barreto August 3, 06:44

    I am grateful for this article, finding a website of the author of the book to help me further strengthen my knowledge in my career Cisco has been very good, Thank you Mr Odom

    Reply to this comment
  7. Mike Cullins April 10, 17:04

    If both Application & Transport are correct (which I agree with), why is the stated answer only ‘B’?

    Reply to this comment
    • certskills Author April 13, 13:22

      The listed answers, just under the “Answers” heading, are A and B. I’m not seeing what you’re reading to land on the idea that the stated answer is only B. Feel free to follow up and let me know what I’m missing. Thanks, Wendell

      Reply to this comment
  8. Miapeh November 17, 15:39

    Can I please get need to help with accessing the “Do I know this already? quiz. I do see the answers to them but I can not see the quizzes.

    Reply to this comment
    • certskills Author November 17, 19:28

      The “Do I know this already?” (DIKTA) quizzes are pre-chapter quizzes found in the first page or two of every chapter of all Cisco Press Official Cert Guides. So I’m a little confused because you’re leaving a note here on a blog page which isn’t about a question in a DIKTA quiz. But if you’re simply asking about the DIKTA quizzes, and you see the answers listed in the chapter, just scan back a couple of pages and you should see the questions.
      Or give me a little more context and I’ll answer again.

      Reply to this comment
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