Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз: Предмет: Файл:
Cisco Press CCNA ICND 2004 - Cisco Press.pdf
13.19 Mб

C H A P T E R 3

Virtual LANs and Trunking

The topics of virtual LANs (VLANs) and VLAN trunking are both important for the CCNA exams. They might be even more important in real networking jobs. VLANs allow a switch to separate different ports into different groups (different VLANs), thereby keeping the traffic in each VLAN separate from the other traffic. VLANs allow engineers to build networks that meet their design requirements without having to buy a different switch for each group. VLAN trunking allows each VLAN to span multiple switches, with traffic from multiple VLANs crossing the same Ethernet links. VLANs and VLAN trunking are as much a part of most corporate LANs today as is TCP/IP.

This chapter reviews the basic concepts behind VLANs and then adds more-thorough coverage of VLAN trunking as compared with the CCNA INTRO Exam Certifiation Guide. Also, this chapter explains VLAN Trunking Protocol (VTP), a Cisco-proprietary protocol that helps you reduce errors when you’re configuring VLANs. This chapter ends with some switch configuration examples.

“Do I Know This Already?” Quiz

The purpose of the “Do I Know This Already?” quiz is to help you decide if you need to read the entire chapter. If you intend to read the entire chapter, you do not necessarily need to answer these questions now.

The eight-question quiz, derived from the major sections in the “Foundation Topics” section, helps you determine how to spend your limited study time.

Table 3-1 outlines the major topics discussed in this chapter and the “Do I Know This Already?” quiz questions that correspond to those topics.

Table 3-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

Foundations Topics Section

Questions Covered in This Section



Review of Virtual LAN Concepts

1 and 2



Trunking with ISL and 802.1Q

3, 4, and 5



VLAN Trunking Protocol (VTP)

6 and 7



VLAN and Trunking Configuration




68 Chapter 3: Virtual LANs and Trunking

CAUTION The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you don’t know the answer to a question or you’re only partially sure of the answer, you should mark this question as wrong for purposes of the self-assessment. Giving yourself credit for an answer you guess correctly skews your self-assessment results and might give you a false sense of security.

1.In a LAN, which of the following terms best equates to the term “VLAN”?

a.Collision domain

b.Broadcast domain

c.Subnet domain

d.Single switch


2.Imagine a switch with three configured VLANs. How many IP subnets are required, assuming that all hosts in all VLANs want to use TCP/IP?





e.You can’t tell from the information provided.

3.Which of the following fully encapsulates the original Ethernet frame in a trunking header?




d.Both ISL and 802.1Q

e.None of the above

4.Which of the following adds the trunking header for all VLANs except one?




d.Both ISL and 802.1Q

e.None of the above

“Do I Know This Already?” Quiz 69

5.Which of the following allows a spanning tree instance per VLAN?




d.Both ISL and 802.1Q

e.None of the above

6.Which of the following advertises VLAN information to neighboring switches?




d.Both ISL and 802.1Q

e.None of the above

7.Which of the following VTP modes allow VLANs to be created on a switch?





e.None of the above

8.Imagine that you are told that switch 1 is configured with the auto parameter for trunking on its Ethernet connection to switch 2. You have to configure switch 2. Which of the following settings for trunking could allow trunking to work?

a.Trunking turned on




e.None of the above

70 Chapter 3: Virtual LANs and Trunking

The answers to the “Do I Know This Already?” quiz appear in Appendix A. The suggested choices for your next step are as follows:

6 or less overall score—Read the entire chapter. This includes the “Foundation Topics,” “Foundation Summary,” and “Q&A” sections.

7 or 8 overall score—If you want more review on these topics, skip to the “Foundation Summary” section and then go to the “Q&A” section. Otherwise, move to the next chapter.