Virtual LANs and VLAN Trunking

Blueprint topics covered in this chapter:

This chapter covers the following subtopics from the Cisco CCIE Routing and Switching written exam blueprint. Refer to the full blueprint in Table I-1 in the Introduction for more details on the topics covered in each chapter and their context within the blueprint.

• VLANs
• VLAN Trunking Protocol (VTP)
• Etherchannel
• PPP over Ethernet (PPPoE)

This chapter continues with the coverage of some of the most fundamental and important LAN topics with coverage of VLANs and VLAN trunking. As usual, for those of you current in your knowledge of the topics in this chapter, review the items next to the Key Topic icons spread throughout the chapter, plus the "Foundation Summary" and "Memory Builders" sections at the end of the chapter.

"Do I Know This Already?" Quiz

Table 2-1 outlines the major headings in this chapter and the corresponding "Do I Know This Already?" quiz questions.

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

In order to best use this pre-chapter assessment, remember to score yourself strictly. You can find the answers in Appendix A, "Answers to the 'Do I Know This Already?' Quizzes."

1. Assume that VLAN 28 does not yet exist on Switch1. Which of the following commands, issued from any part of global configuration mode (reached with the configure terminal exec command) would cause the VLAN to be created?

   1. vlan 28
   2. vlan 28 name fred
   3. switchport vlan 28
   4. switchport access vlan 28
   5. switchport access 28

2. Which of the following are the two primary motivations for using private VLANs?

   1. Better LAN security
   2. IP subnet conservation
   3. Better consistency in VLAN configuration details
   4. Reducing the impact of broadcasts on end-user devices
   5. Reducing the unnecessary flow of frames to switches that do not have any ports in the VLAN to which the frame belongs

3. Which of the following VLANs can be pruned by VTP on an 802.1Q trunk?

   1. 1–1023
   2. 1–1001
   3. 2–1001
   4. 1–1005
   5. 2–1005

4. An existing switched network has ten switches, with Switch1 and Switch2 being the only VTP servers in the network. The other switches are all VTP clients and have successfully learned about the VLANs from the VTP servers. The only configured VTP parameter on all switches is the VTP domain name (Larry). The VTP revision number is 201. What happens when a new, already-running VTP client switch, named Switch11, with domain name Larry and revision number 301, connects via a trunk to any of the other ten switches?

   1. No VLAN information changes; Switch11 ignores the VTP updates sent from the two existing VTP servers until the revision number reaches 302.
   2. The original ten switches replace their old VLAN configuration with the configuration in Switch11.
   3. Switch11 replaces its own VLAN configuration with the configuration sent to it by one of the original VTP servers.
   4. Switch11 merges its existing VLAN database with the database learned from the VTP servers, because Switch11 had a higher revision number.

5. An existing switched network has ten switches, with Switch1 and Switch2 being the only VTP servers in the network. The other switches are all VTP clients, and have successfully learned about the VLANs from the VTP server. The only configured VTP parameter is the VTP domain name (Larry). The VTP revision number is 201. What happens when an already-running VTP server switch, named Switch11, with domain name Larry and revision number 301, connects via a trunk to any of the other ten switches?

   1. No VLAN information changes; all VTP updates between the original VTP domain and the new switch are ignored.
   2. The original ten switches replace their old VLAN configuration with the configuration in Switch11.
   3. Switch11 replaces its old VLAN configuration with the configuration sent to it by one of the original VTP servers.
   4. Switch11 merges its existing VLAN database with the database learned from the VTP servers, because Switch11 had a higher revision number.
   5. None of the other answers is correct.

6. Assume that two brand-new Cisco switches were removed from their cardboard boxes. PC1 was attached to one switch, PC2 was attached to the other, and the two switches were connected with a cross-over cable. The switch connection dynamically formed an 802.1Q trunk. When PC1 sends a frame to PC2, how many additional bytes of header are added to the frame before it passes over the trunk?

   1. 0
   2. 4
   3. 8
   4. 26

7. Assume that two brand-new Cisco Catalyst 3550 switches were connected with a cross-over cable. Before attaching the cable, one switch interface was configured with the switchport trunk encapsulation dot1q, switchport mode trunk, and switchport nonegotiate subcommands. Which of the following must be configured on the other switch before trunking will work between the switches?

   1. switchport trunk encapsulation dot1q
   2. switchport mode trunk
   3. switchport nonegotiate
   4. No configuration is required.

8. When configuring trunking on a Cisco router fa0/1 interface, under which configuration modes could the IP address associated with the native VLAN (VLAN 1 in this case) be configured?

   1. Interface fa 0/1 configuration mode
   2. Interface fa 0/1.1 configuration mode
   3. Interface fa 0/1.2 configuration mode
   4. None of the other answers is correct

9. Which of the following is false about 802.1Q?

   1. Encapsulates the entire frame inside an 802.1Q header and trailer
   2. Supports the use of a native VLAN
   3. Allows VTP to operate only on extended-range VLANs
   4. Is chosen over ISL by DTP

10. Which command enables PPPoE on the outside Ethernet interface on a Cisco router?

    1. pppoe enable
    2. pppoe-client enable
    3. pppoe-client dialer-pool-number
    4. pppoe-client dialer-number