CCENT/CCNA ICND1 Official Exam Certification Guide - Chapter 5

Fundamentals of IP Addressing and Routing OSI vật lý lớp (Layer 1) định nghĩa như thế nào để truyền tải các bit trên một loại mạng vật lý. OSI lớp liên kết dữ liệu (Layer 2) xác định khung, địa chỉ, phát hiện lỗi, và các quy tắc khi sử dụng các phương tiện vật lý. Mặc dù họ là quan trọng, hai lớp này không xác định làm thế nào để cung cấp dữ liệu giữa các thiết bị tồn tại xa nhau, với nhiều mạng vật lý khác nhau ngồi giữa hai máy tính. Chương này giải...
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CCENT/CCNA ICND1 Official Exam Certification Guide - Chapter 5 1828xbook.fm Page 93 Thursday, July 26, 2007 3:10 PM 5 CHAPTER Fundamentals of IP Addressing and Routing The OSI physical layer (Layer 1) defines how to transmit bits over a particular type of physical network. The OSI data link layer (Layer 2) defines the framing, addressing, error detection, and rules for when to use the physical medium. Although they are important, these two layers do not define how to deliver data between devices that exist far from each other, with many different physical networks sitting between the two computers. This chapter explains the function and purpose of the OSI network layer (Layer 3): the end-to-end delivery of data between two computers. Regardless of the type of physical network to which each endpoint computer is attached, and regardless of the types of physical networks used between the two computers, the network layer defines how to forward, or route, data between the two computers. This chapter covers the basics of how the network layer routes data packets from one computer to another. After reviewing the full story at a basic level, this chapter examines in more detail the network layer of TCP/IP, including IP addressing (which enables efficient routing), IP routing (the forwarding process itself), IP routing protocols (the process by which routers learn routes), and several other small but important features of the network layer. “Do I Know This Already?” Quiz The “Do I Know This Already?” quiz allows you to assess whether you should read the entire chapter. If you miss no more than one of these 13 self-assessment questions, you might want to move ahead to the “Exam Preparation Tasks” section. Table 5-1 lists the major headings in this chapter and the “Do I Know This Already?” quiz questions covering the material in those sections. This helps you assess your knowledge of these specific areas. The answers to the “Do I Know This Already?” quiz appear in Appendix A. 1828xbook.fm Page 94 Thursday, July 26, 2007 3:10 PM 94 Chapter 5: Fundamentals of IP Addressing and Routing “Do I Know This Already?” Foundation Topics Section-to-Question Mapping Table 5-1 Foundation Topics Section Questions Overview of Network Layer Functions 1–3 IP Addressing 4–8 IP Routing 9, 10 IP Routing Protocols 11 Network Layer Utilities 12, 13 Which of the following are functions of OSI Layer 3 protocols? 1. Logical addressing a. Physical addressing b. Path selection c. Arbitration d. Error recovery e. Imagine that PC1 needs to send some data to PC2, and PC1 and PC2 are separated by 2. several routers. What are the largest entities that make it from PC1 to PC2? Frame a. Segment b. Packet c. L5 PDU d. L3 PDU e. L1 PDU f. Imagine a network with two routers that are connected with a point-to-point HDLC 3. serial link. Each router has an Ethernet, with PC1 sharing the Ethernet with Router1, and PC2 sharing the Ethernet with Router2. When PC1 sends data to PC2, which of the following is true? Router1 strips the Ethernet header and trailer off the frame received from PC1, a. never to be used again. Router1 encapsulates the Ethernet frame inside an HDLC header and sends the b. frame to Router2, which extracts the Ethernet frame for forwarding to PC2. 1828xbook.fm Page 95 Thursday, July 26, 2007 3:10 PM “Do I Know This Already?” Quiz 95 Router1 strips the Ethernet header and trailer off the frame received from PC1, ...