Chapter 8


What is a VLAN?


Answer: A virtual LAN, or VLAN, is a group of computers, network printers, network servers, and other network devices behaving as if they were connected to a single network segment. A VLAN might also be considered a broadcast domain.


What is the IEEE standard for virtual LANs?


Answer: IEEE 802.1q.


What advantages are provided by VLANs?


Answer: VLANs provide the following advantages:

- Help make Layer 2 networks scalable

- Isolate problems within a small part of the network

- Remove the physical network boundaries, enabling users and servers to be located anywhere.

- Enhance network security through logical segmentation of users and groups

- Increase performance by containing broadcast traffic


Name the three types of VLANs and explain their differences.


Answer: Port based, address based, and Layer 3 based. Port-based VLAN membership is based on the switch port. Address-based VLAN membership is based on the MAC, or hardware, address of the connecting device. Layer 3-based VLAN membership is based on the network address of the connecting device.


What is a Layer 3 switch?


Answer: Switches work at Layer 2 of the OSI model, the data link layer, using MAC addresses to the determine source and destination of the network traffic. Routers work at Layer 3 of the OSI model, the network layer, using Layer 3 (network) addresses, such as an IP address, to determine the source and destination of the network traffic. The difference between a Layer 3 switch and a router is that the switch uses a different algorithm to decide how to forward packets across the network. In contrast, routers forward packets based on algorithms that are determined by the routing protocol.


How can you communicate between VLANs?


Answer: Because direct communication between VLANs is not possible within a switch, a Layer 3 device is required to forward the traffic between VLANs. Each VLAN is a broadcast domain and uses Layer 2 (MAC) addressing to determine the source and destination of each frame, whereas a Layer 3 device, such as a router or Layer 3 switch, uses the network address to determine the source and destination of the traffic. Traffic can be forwarded between VLANs because Layer 3 looks beyond the broadcast domains.


How might you extend a VLAN?


Answer: You can extend a VLAN beyond the switch by using a trunk link.


What's the difference between an access link and a trunk link?


Answer: Access links are interfaces that belong to only one VLAN, whereas trunk links transport traffic from multiple VLANs between switches.


What is VLAN tagging?


Answer: VLAN tagging is used to identify the VLAN to which frames belong as they are received by a switch from across the trunk link connecting two switches together.


Which VLAN tagging method is an open standard? What is the benefit of using open standards?


Answer: The open standard for VLAN tagging is IEEE 802.1q. The benefit of using open standards is that it ensures interoperability between differing vendor equipment, such as a switch from ABC Company and a switch from XYZ Corporation.


What is a VTP management domain?


Answer: A VTP management domain is a group of switches sharing VTP information with each other.


How many VTP modes are there? What are they, and when would each be used?


Answer: Four: Server mode, client mode, transparent mode, and off.

Server mode might be considered the master switch in that all changes within the VTP management domain originate from a switch in server mode.

Client mode forwards updates to other devices, even though it cannot make changes.

Transparent mode receives VTP management domain, such as additions, deletions, and other changes, from the server mode switch. Switches configured for transparent mode do not process these updates; instead, the switch just passes the updates along. Off mode disables VTP completely on the switch.


Which VTP mode is the default mode?


Answer: Server mode.