The TCP/IP and OSI Networking Models

You can think of a networking model as you think of a set of architectural plans for building a house. Sure, you can build a house without the architectural plans, but it will work better if you follow the plans. And because you probably have a lot of different people working on building your house, such as framers, electricians, bricklayers, painters, and so on, it helps if they can all reference the same plan. Similarly, you could build your own network, write your own software, build your own networking cards, and create a network without using any existing networking model. However, it is much easier to simply buy and use products that already conform to some well-known networking model. Because the networking product vendors use the same networking model, their products should work well together.

The CCNA exams include detailed coverage of one networking model: Transmission Control Protocol/Internet Protocol (TCP/IP). TCP/IP is the most pervasively used networking model in the history of networking. You can find support for TCP/IP on practically every computer operating system (OS) in existence today, from mobile phones to mainframe computers. Every network built using Cisco products today supports TCP/IP. And not surprisingly, the CCNA exams focus heavily on TCP/IP.

The ICND1 exam, and the ICND2 exam to a small extent, also covers a second networking model, called the Open System Interconnection (OSI) reference model. Historically, OSI was the first large effort to create a vendor-neutral networking model. Because of that timing, many of the terms used in networking today come from the OSI model, so this chapter’s section on OSI discusses OSI and the related terminology.

“Do I Know This Already?” Quiz

The “Do I Know This Already?” quiz allows you to assess if you should read the entire chapter. If you miss no more than one of these ten self-assessment questions, you might want to move ahead to the “Exam Preparation Tasks” section. Table 2-1 lists the major headings in this chapter and the “Do I Know This Already?” quiz questions covering the material in those headings so you can assess your knowledge of these specific areas. The answers to the “Do I Know This Already?” quiz appear in Appendix A, “Answers to the ‘Do I Know This Already?’ Quizzes.”

Table 2-1 Do I Know This Already?” Foundation Topics Section-to-Question Mapping

1. Which of the following protocols are examples of TCP/IP transport layer protocols? (Choose two answers.)

   1. Ethernet
   2. HTTP
   3. IP
   4. UDP
   5. SMTP
   6. TCP

2. Which of the following protocols are examples of TCP/IP network access layer protocols? (Choose two answers.)

   1. Ethernet
   2. HTTP
   3. IP
   4. UDP
   5. SMTP
   6. TCP
   7. PPP

3. The process of HTTP asking TCP to send some data and making sure that it is received correctly is an example of what?

   1. Same-layer interaction
   2. Adjacent-layer interaction
   3. OSI model
   4. All of these answers are correct.

4. The process of TCP on one computer marking a TCP segment as segment 1, and the receiving computer then acknowledging the receipt of TCP segment 1 is an example of what?

   1. Data encapsulation
   2. Same-layer interaction
   3. Adjacent-layer interaction
   4. OSI model
   5. All of these answers are correct.

5. The process of a web server adding a TCP header to the contents of a web page, followed by adding an IP header, and then adding a data link header and trailer is an example of what?

   1. Data encapsulation
   2. Same-layer interaction
   3. OSI model
   4. All of these answers are correct.

6. Which of the following terms is used specifically to identify the entity created when encapsulating data inside data link layer headers and trailers?

   1. Data
   2. Chunk
   3. Segment
   4. Frame
   5. Packet
   6. None of these—there is no encapsulation by the data link layer.

7. Which OSI layer defines the functions of logical network-wide addressing and routing?

   1. Layer 1
   2. Layer 2
   3. Layer 3
   4. Layer 4
   5. Layer 5
   6. Layer 6
   7. Layer 7

8. Which OSI layer defines the standards for cabling and connectors?

   1. Layer 1
   2. Layer 2
   3. Layer 3
   4. Layer 4
   5. Layer 5
   6. Layer 6
   7. Layer 7

9. Which OSI layer defines the standards for data formats and encryption?

   1. Layer 1
   2. Layer 2
   3. Layer 3
   4. Layer 4
   5. Layer 5
   6. Layer 6
   7. Layer 7

10. Which of the following terms are not valid terms for the names of the seven OSI layers? (Choose two answers.)

    1. Application
    2. Data link
    3. Transmission
    4. Presentation
    5. Internet
    6. Session