A: TCP/IP Model Lingo

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

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.