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Foundation Summary 89

Foundation Summary

The “Foundation Summary” section lists the most important facts from the chapter. Although this section does not list everything that will be on the exam, a well-prepared CCNA candidate should at a minimum know all the details in each Foundation Summary before taking the exam.

Figure 3-10 shows the general idea of a VLAN, showing two different VLANs/broadcast domains.

Figure 3-10 Network with Two VLANs Using One Switch

Dino

VLAN 1

Fred

Wilma

VLAN 2

Table 3-6 summarizes the key features and points of comparison between ISL and 802.1Q.

Table 3-6

ISL and 802.1Q Compared

 

 

 

 

 

 

 

Function

ISL

802.1Q

 

 

 

 

 

Standards body that defines the protocol

Cisco-proprietary

IEEE

 

 

 

 

 

Encapsulates the original frame

Yes

No

 

 

 

 

 

Allows multiple spanning trees

Yes

No

 

 

 

 

 

Uses a native VLAN

No

Yes

 

 

 

 

90 Chapter 3: Virtual LANs and Trunking

Table 3-7 offers a comparative overview of the three VTP modes.

Table 3-7 VTP Modes

 

Server

Client

Transparent

Function

Mode

Mode

Mode

 

 

 

 

Originates VTP advertisements

Yes

No

No

 

 

 

 

Processes received advertisements and synchronizes

Yes

Yes

No

VLAN configuration information with other switches

 

 

 

 

 

 

 

Forwards VTP advertisements received in a trunk

Yes

Yes

Yes

 

 

 

 

Saves VLAN configuration in NVRAM

Yes

No

Yes

 

 

 

 

Can create, modify, or delete VLANs using configuration

Yes

No

Yes

commands

 

 

 

 

 

 

 

Table 3-8 summarizes the different trunking options on the 2950 and their meanings.

Table 3-8 2950 Trunk Configuration Options with the switchport mode Command

Option

Description

 

 

access

Disables port trunk mode and does not even attempt to form a trunk on

 

the interface.

 

 

trunk

Configures the port into permanent trunk mode and negotiates with the

 

connected device to decide whether to use 802.1Q or ISL.

 

 

dynamic desirable

Triggers the port to negotiate the link from nontrunking to trunk mode.

 

The port negotiates to a trunk port if the connected device is either in the

 

trunk, dynamic desirable, or dynamic auto state. Otherwise, the port

 

becomes a nontrunk port.

 

 

dynamic auto

Lets a port become a trunk only if the connected device has the state set

 

to dynamic desirable or trunk.

 

 

Q&A 91

Q&A

As mentioned in the Introduction, you have two choices for review questions. The following questions give you a bigger challenge than the exam because they are open-ended. By reviewing with this more-difficult question format, you can exercise your memory better and prove your conceptual and factual knowledge of the topics covered in this chapter. The answers to these questions are found in Appendix A.

For more practice with exam-like question formats, including multiple-choice questions and those using a router simulator, use the exam engine on the CD.

1.Define broadcast domain.

2.Define VLAN.

3.If two Cisco LAN switches are connected using Fast Ethernet, what VLAN trunking protocols can be used? If only one VLAN spans both switches, is a VLAN trunking protocol needed?

4.Define VTP.

5.Name the three VTP modes. Which mode does not allow VLANs to be added or modified?

6.What Catalyst 2950 switch command configures ISL trunking on fastethernet port 0/12, so that as long as the switch port on the other end of the trunk is not disabled (off) or configured to not negotiate to become a trunk, the trunk is definitely placed in trunking mode?

7.What type of VTP mode allows a switch to create VLANs and advertise them to other switches?

8.Must all members of the same VLAN be in the same collision domain, the same broadcast domain, or both?

9.What is Cisco’s proprietary trunking protocol over Ethernet?

10.Explain the benefits provided by VTP pruning.

11.Consider the phrase “A VLAN is a broadcast domain is an IP subnet.“ Do you agree or disagree? Why?

12.What fields are added or changed in an Ethernet header when you use 802.1Q? Where is the VLAN ID in those fields?

92Chapter 3: Virtual LANs and Trunking

13.Explain how a switch in VTP transparent mode treats VTP messages received from a VTP server.

14.What command on a 2950 switch creates VLAN 5? What configuration mode is required?

15.What command on a 2950 switch puts an interface into VLAN 5? What configuration mode is required?

16.Describe the basic differences in the processes used by VLAN configuration mode and the normally used configuration mode.

17.Give the correct syntax for the commands that put an interface into the various trunking modes, and identify which commands work when the switch on the other side of the link uses the auto option.

18.What 2950 show commands list trunk status, both configured and operational?

Cisco Published ICND Exam Topics*

Covered in This Part:

2Design an IP addressing scheme to support classful, classless, and private addressing to meet design requirements

3Select an appropriate routing protocol based on user requirements

7Configure routing protocols given user requirements

8Configure IP addresses, subnet masks, and gateway addresses on routers and hosts

9Configure a router for additional administrative functionality

15 Utilize the OSI model as a guide for systematic network troubleshooting

17Troubleshoot routing protocols

18Troubleshoot IP addressing and host configuration

19Troubleshoot a device as part of a working network

24Evaluate the characteristics of routing protocols

* Always re-check www.cisco.com for the latest posted exam topics