CSMA/CD, Switching, and VLANs

Question 1

What is the purpose of CSMA/CD in Ethernet networks?

Answer 1

To detect and handle data collisions

Question 2

When does a device transmit on a CSMA/CD network?

Answer 2

After sensing that the channel is idle

Question 3

What does a device do after a collision is detected?

Answer 3

Sends a jam signal and waits a random time

Question 4

On which types of Ethernet is CSMA/CD required?

Answer 4

Half-duplex Ethernet

Question 5

Why is CSMA/CD unnecessary in full-duplex Ethernet?

Answer 5

No collisions occur

Question 6

Which layer of the OSI model is CSMA/CD associated with?

Answer 6

Data Link

Question 7

What is a ‘jam signal’?

Answer 7

A signal to stop data transmission

Question 8

What algorithm is used after a collision is detected in CSMA/CD?

Answer 8

Backoff algorithm

Question 9

What technology has largely replaced CSMA/CD in modern LANs?

Answer 9

Full-duplex Ethernet switching

Question 10

What topology did early Ethernet use that required CSMA/CD?

Answer 10

Bus

Question 11

What does a switch use to forward frames?

Answer 11

MAC addresses

Question 12

What table does a switch build to make forwarding decisions?

Answer 12

MAC address table

Question 13

What is microsegmentation?

Answer 13

Isolating each port into its own collision domain

Question 14

What happens if a switch doesn’t know the destination MAC address?

Answer 14

Floods it out all ports except the incoming port

Question 15

Which device creates multiple collision domains by default?

Answer 15

Switch

Question 16

What is the main difference between a switch and a hub?

Answer 16

Switches forward based on MAC addresses

Question 17

What is store-and-forward switching?

Answer 17

The switch stores and checks the frame before forwarding

Question 18

What type of switch port carries traffic from multiple VLANs?

Answer 18

Trunk port

Question 19

What does STP (Spanning Tree Protocol) prevent?

Answer 19

Broadcast storms

Question 20

Which command shows the MAC address table on a Cisco switch?

Answer 20

show mac address-table

Question 21

How many collision domains exist in a 24-port switch?

Answer 21

24

Question 22

How does a switch learn a MAC address?

Answer 22

Observing source MAC addresses in frames

Question 23

What is the default action of a switch for unknown unicast frames?

Answer 23

Flood to all ports

Question 24

Which protocol prevents Layer 2 loops in switched networks?

Answer 24

STP

Question 25

What is the benefit of full-duplex mode on a switch port?

Answer 25

Eliminates collisions

Question 26

What is the purpose of VLANs?

Answer 26

Segment a network logically

Question 27

Which device is needed for inter-VLAN communication?

Answer 27

Router or Layer 3 switch

Question 28

What protocol is used for VLAN tagging?

Answer 28

802.1Q

Question 29

What VLAN number is the default VLAN on Cisco switches?

Answer 29

1

Question 30

What is the function of a trunk link?

Answer 30

Carries traffic for multiple VLANs

Question 31

What type of port is configured for a single VLAN only?

Answer 31

Access

Question 32

Which command sets a port as an access port?

Answer 32

switchport mode access

Question 33

What is the purpose of the native VLAN on a trunk link?

Answer 33

To carry untagged frames

Question 34

Which protocol distributes VLAN information across switches?

Answer 34

VTP

Question 35

What are the three VTP modes?

Answer 35

Server, Client, Transparent

Question 36

What is a broadcast domain in switching?

Answer 36

A group of devices in the same subnet

Question 37

What is VLAN hopping?

Answer 37

A security exploit

Question 38

How do you verify VLAN configuration on a switch?

Answer 38

show vlan brief

Question 39

How many usable VLANs are defined in the IEEE 802.1Q standard?

Answer 39

4094

Question 40

What happens to a frame tagged with an unallowed VLAN on a trunk port?

Answer 40

It is dropped

Question 41

What does a Layer 3 switch offer beyond Layer 2 switching?

Answer 41

Routing capability

Question 42

Which VLAN ID is reserved and cannot be used?

Answer 42

0

Question 43

What does 'Dynamic Auto' mode do in switch port configuration?

Answer 43

Responds to trunk negotiation

Question 44

What causes a VLAN mismatch on a trunk link?

Answer 44

Different native VLANs on each end

Question 45

What is the purpose of the 'switchport trunk encapsulation dot1q' command?

Answer 45

Sets trunking protocol

Question 46

What is the VLAN ID range for extended VLANs?

Answer 46

1006–4094

Question 47

What happens if you don't assign a port to a VLAN explicitly?

Answer 47

It defaults to VLAN 1

Question 48

What is the maximum number of VLANs supported by 802.1Q?

Answer 48

4096

Question 49

Which command displays trunk status?

Answer 49

show interface trunk

Question 50

Which feature can restrict a switch port to specific MAC addresses?

Answer 50

Port Security

Question 51

Switches contain a memory chip known as an _______, which builds a table listing which device is plugged into which port.

Answer 51

CAM (Content Addressable Memory)

Question 52

Which two commands add an IP address to the VLAN?

Answer 52

interface vlan 1 ip address [IP] [SUBNET]

Question 53

Which commands will enable Telnet and add a password to the switch Telnet lines?

Answer 53

line vty 0 4 password YOUR_PASSWORD login

Question 54

How do you permit only SSH traffic into your Telnet lines?

Answer 54

line vty 0 4 transport input ssh

Question 55

What is the most likely cause of Telnet to another switch not working?

Answer 55

No IP address configured on the VLAN interface

Question 56

Switches remember all VLAN info, even when reloaded. True or False?

Answer 56

True

Question 57

A switch interface can be in which of three modes?

Answer 57

Access Trunk Dynamic (Auto or Desirable)