Chapter 11: Implementing Ethernet Virtual LANs Flashcards
In a LAN, which of the following terms best equates to the term VLAN?
a. Collision domain
b. Broadcast domain
c. Subnet
d. Single switch
e. Trunk
B
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?
a. 0
b. 1
c. 2
d. 3
e. You cannot tell from the information provided.
D
Switch SW1 sends a frame to switch SW2 using 802.1Q trunking. Which of the answers describes how SW1 changes or adds to the Ethernet frame before forwarding the frame to SW2?
a. Inserts a 4-byte header and does change the MAC addresses
b. Inserts a 4-byte header and does not change the MAC addresses
c. Encapsulates the original frame behind an entirely new Ethernet header
d. None of the other answers are correct
B
Imagine that you are told that switch 1 is configured with the dynamic auto param- eter for trunking on its Fa0/5 interface, which is connected to switch 2. You have to configure switch 2. Which of the following settings for trunking could allow trunking to work? (Choose two answers.)
a. on
b. dynamic auto
c. dynamic desirable
d. access
e. None of the other answers are correct.
A,C
A switch has just arrived from Cisco. The switch has never been configured with any VLANs, but VTP has been disabled. An engineer gets into configuration mode and issues the vlan 22 command, followed by the name Hannahs-VLAN command. Which of the following are true? (Choose two answers.)
a. VLAN 22 is listed in the output of the show vlan brief command.
b. VLAN 22 is listed in the output of the show running-config command.
c. VLAN 22 is not created by this process.
d. VLAN 22 does not exist in that switch until at least one interface is assigned to that VLAN.
A,B
Which of the following commands identify switch interfaces as being trunking inter- faces: interfaces that currently operate as VLAN trunks? (Choose two answers.)
a. show interfaces
b. show interfaces switchport
c. show interfaces trunk
d. show trunks
B,C
the concept of a virtual LAN:
A LAN includes all devices in the same broadcast domain.
summarize the most common reasons for choosing to create smaller broadcast domains (VLANs):
■ To reduce CPU overhead on each device by reducing the number of devices that receive each broadcast frame
■ To reduce security risks by reducing the number of hosts that receive copies of frames that the switches flood (broadcasts, multicasts, and unknown unicasts)
■ To improve security for hosts that send sensitive data by keeping those hosts on a sepa- rate VLAN
■ To create more flexible designs that group users by department, or by groups that work together, instead of by physical location
■ To solve problems more quickly, because the failure domain for many problems is the same set of devices as those in the same broadcast domain
■ To reduce the workload for the Spanning Tree Protocol (STP) by limiting a VLAN to a single access switch
VLAN trunking
VLAN trunking causes the switches to use a process called VLAN tagging, by which the sending switch adds another header to the frame before sending it over the trunk.
describe how 802.1Q trunking tags a frame for trunking
802.1Q inserts an extra 4-byte 802.1Q VLAN header into the original frame’s Ethernet header. The 12-bit field inside the header supports a theoretical maximum of 2(12) (4096) VLANs, but in practice it sup- ports a maximum of 4094. (Both 802.1Q and ISL use 12 bits to tag the VLAN ID, with two reserved values [0 and 4095].)
How does Cisco break up the ranges of available VLAN id’s?
two ranges: the normal range and the extended range. All switches can use normal-range VLANs with values from 1 to 1005. Only some switches can use extended-range VLANs with VLAN IDs from 1006 to 4094. The rules for which switches can use extended-range VLANs depend on the con- figuration of the VLAN Trunking Protocol
Describe the use of the 802.1Q native VLAN
802.1Q also defines one special VLAN ID on each trunk as the native VLAN (defaulting
to use VLAN 1). By definition, 802.1Q simply does not add an 802.1Q header to frames in the native VLAN. When the switch on the other side of the trunk receives a frame that does not have an 802.1Q header, the receiving switch knows that the frame is part of the native VLAN. Note that because of this behavior, both switches must agree on which VLAN is the native VLAN. The 802.1Q native VLAN provides some interesting functions, mainly to support connec- tions to devices that do not understand trunking.
Describe the relationship between VLANS and Subnets in a network, specifically how they map to each other with respect to routing.
When including VLANs in a campus LAN design, the devices in a VLAN need to be in the same subnet. Following the same design logic, devices in different VLANs need to be in dif- ferent subnets.
Describe the steps to configure a new VLAN and add the access interfaces to it.
Step 1.
To configure a new VLAN, follow these steps:
A. From configuration mode, use the vlan vlan-id command in global con- figuration mode to create the VLAN and to move the user into VLAN con- figuration mode.
B. (Optional)UsethenamenamecommandinVLANconfigurationmode to list a name for the VLAN. If not configured, the VLAN name is VLANZZZZ, where ZZZZ is the four-digit decimal VLAN ID.
Step 2.
For each access interface (each interface that does not trunk, but instead belongs to a single VLAN), follow these steps:
A. Use the interface type number command in global configuration mode to move into interface configuration mode for each desired interface.
B. Usethe switchport access vlan id-number command in interface configuration mode to specify the VLAN number associated with that interface.
C. (Optional) Use the switchport mode access command in interface configuration mode to make this port always operate in access mode (that is, to not trunk).
VLAN trunking protocol:
VTP is a Cisco propri- etary tool on Cisco switches that advertises each VLAN configured in one switch (with the vlan number command) so that all the other switches in the campus learn about that VLAN.
Describe how to check the VTP status,what the status types are, and which
switch VTP status can configure which range of VLANS
Check the VTP status with the show vtp status command.
If your switch uses VTP server or client mode, you will find:
■ The server switches can configure VLANs in the standard range only (1–1005).
■ The client switches cannot configure VLANs.
■ Both servers and clients may be learning new VLANs from other switches, and seeing their VLANs deleted by other switches, because of VTP.
■ The show running-config command does not list any vlan commands.
describe the command and parameters used to set up the type of trunking used.
Switches that support both types of trunking use the switchport trunk encapsulation {dot1q | isl | negotiate} inter- face subcommand to either configure the type or allow DTP to negotiate the type.
List the different types of administrative trunking modes as well as the command to set them.
access: Always act as an access (nontrunk) port
trunk: Always act as a trunk port
dynamic desirable: nitiates negotiation messages and responds to negotiation messages to dynamically choose whether to start using trunking
dynamic auto: Passively waits to receive trunk negotiation messages, at which point the switch will respond and negotiate whether to use trunking
Cisco switches use the switchport mode interface subcommand to define the administrative trunking mode
Explain the difference between the administrative mode and the operational mode on a switchport
The administrative mode refers
to the configuration setting for whether trunking should be used. Each interface also has an operational mode, which refers to what is currently happening on the interface, and might have been chosen by DTP’s negotiation with the other device.
Expected Trunking Operational Mode Based on the Configured Administrative Modes of Access and Access
Access
