Section 8: Ethernet Switching

Question 1

What is the primary function of CSMA/CD in an Ethernet network?

Answer 1

To manage how devices share a network medium and handle collisions in a contention-based environment.

Question 2

In CSMA/CD, what does ‘Carrier Sense’ refer to?

Answer 2

The process where a device ‘listens’ to the network medium to determine if it is clear before attempting to transmit.

Question 3

What happens immediately after two devices on an Ethernet hub detect a collision?

Answer 3

Both devices stop transmitting and start a random back-off timer before attempting to retransmit.

Question 4

Why is a contention-based method like CSMA/CD generally more efficient for LANs than a deterministic method like Token Ring?

Answer 4

Because it has lower overhead and allows any device to use the full available bandwidth when needed, rather than forcing devices to wait for a token.

Question 5

Which networking device extends a collision domain but does not segment it?

Answer 5

A hub. All ports on a hub belong to the same, single collision domain.

Question 6

Which Layer 2 device creates a separate collision domain for each of its ports?

Answer 6

A switch (or a bridge).

Question 7

What Layer 3 device is used to segment broadcast domains?

Answer 7

A router. A Layer 3 switch can also perform this function.

Question 8

How do VLANs affect broadcast domains on a Layer 2 switch?

Answer 8

VLANs logically divide a switch’s single broadcast domain into multiple, smaller, and separate broadcast domains.

Question 9

At which OSI layer does a hub operate, and what is its primary function?

Answer 9

Layer 1 (Physical). It acts as a multi-port repeater, regenerating a signal and sending it out all of its other ports.

Question 10

How does a Layer 2 switch make its forwarding decisions?

Answer 10

It learns the MAC addresses of connected devices and builds a MAC address table, which it uses to forward frames only to the port associated with the destination MAC address.

Question 11

What is the primary functional difference between a Layer 2 switch and a router regarding network domains?

Answer 11

A Layer 2 switch breaks up collision domains but operates within a single broadcast domain by default. A router breaks up broadcast domains.

Question 12

When would you choose to use a Layer 3 switch instead of a traditional router?

Answer 12

For high-speed inter-VLAN routing on an internal or campus network, as it is generally faster and more efficient for this specific task.

Question 13

What key problem do switches solve that hubs create?

Answer 13

Switches solve the problem of excessive collisions by creating a separate collision domain for each port, whereas hubs consolidate all connected devices into one large collision domain.

Question 14

What is the primary purpose of creating a VLAN on a switch?

Answer 14

To logically segment a network into multiple, separate broadcast domains, which enhances security and improves performance.

Question 15

What OSI layer do VLANs operate at?

Answer 15

Layer 2 (Data Link Layer).

Question 16

What is required for a device in VLAN 10 to communicate with a device in VLAN 20?

Answer 16

A Layer 3 device, such as a router or a Layer 3 switch, is required to perform inter-VLAN routing.

Question 17

What is an SVI, and what role does it play in a VLAN environment?

Answer 17

An SVI (Switch Virtual Interface) is a virtual Layer 3 interface on a switch that provides routing capabilities for the traffic within its associated VLAN.

Question 18

What is the term for a logical grouping of devices that segments a network into separate broadcast domains?

Answer 18

A Virtual Local Area Network (VLAN).

Question 19

What IEEE standard is used for VLAN tagging on trunk links?

Answer 19

IEEE 802.1Q.

Question 20

What does the IEEE 802.1Q standard define?

Answer 20

The process of VLAN tagging, which inserts a VLAN ID into an Ethernet frame, allowing a trunk link to carry traffic for multiple VLANs.

Question 21

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

Answer 21

It carries all untagged traffic, which ensures compatibility with legacy devices that do not support VLAN tagging.

Question 22

Why is it beneficial to place VoIP phones in their own dedicated Voice VLAN?

Answer 22

To separate and prioritize voice traffic from regular data traffic, allowing for the application of Quality of Service (QoS) policies to ensure call quality.

Question 23

What are the two main benefits of using link aggregation?

Answer 23

1. Increased bandwidth capacity by combining multiple physical links into one logical link. 2. Redundancy and higher availability, as traffic can continue flowing if one of the physical links fails.

Question 24

What is a common symptom of a duplex mismatch between two connected switch ports?

Answer 24

Severely degraded network performance, high error counts, and late collisions.

Question 25

What is the primary problem that Spanning Tree Protocol (STP) is designed to solve?

Answer 25

It prevents Layer 2 switching loops in networks that have redundant physical paths.

Question 26

What protocol prevents switching loops in a redundant Layer 2 topology?

Answer 26

Spanning Tree Protocol (STP), also known by the IEEE standard 802.1d.

Question 27

How does STP determine which switch in a network will become the root bridge?

Answer 27

STP elects the switch with the lowest Bridge ID (BID). The BID is composed of a priority value and the switch's MAC address.

Question 28

What is the function of a 'Non-Designated' or 'Blocking' port in an STP topology?

Answer 28

It logically blocks traffic to prevent a loop from forming but remains available to transition to a forwarding state if an active link in the network fails.

Question 29

What are the four operational states a port transitions through in STP?

Answer 29

Blocking, Listening, Learning, and Forwarding.

Question 30

In STP, what is the relationship between a link's speed and its path cost?

Answer 30

It is an inverse relationship: higher speed links have a lower cost, and lower speed links have a higher cost.

Question 31

What is the fundamental goal of Network Access Control (NAC)?

Answer 31

To increase network security by inspecting devices as they connect and enforcing security policies before granting them access to the network.

Question 32

What are the three main components involved in an 802.1X authentication transaction?

Answer 32

1. The Supplicant (the client device), 2. The Authenticator (the switch or WAP), and 3. The Authentication Server (e.g., a RADIUS server).

Question 33

What is the difference between a persistent and a non-persistent NAC agent?

Answer 33

A persistent agent is software permanently installed on a device (like a company-owned computer) for continuous monitoring. A non-persistent agent runs temporarily to assess compliance (e.g., on a BYOD device) and is removed after the scan is complete.

Question 34

If a device fails a NAC posture assessment, where is it typically placed?

Answer 34

It is placed into a quarantine network, which is a segregated VLAN used for remediation.

Question 35

What does the term Maximum Transmission Unit (MTU) refer to?

Answer 35

The largest size of a data frame, measured in bytes, that can be sent over a specific network link.

Question 36

What is the standard MTU size for a wired Ethernet network?

Answer 36

1500 bytes.

Question 37

What is the term for a frame that exceeds the standard Ethernet MTU size of 1500 bytes?

Answer 37

A Jumbo Frame.

Question 38

What is a 'jumbo frame' and what is its typical size?

Answer 38

A frame that exceeds the standard 1500-byte MTU. Its size is typically configured to 9000 bytes and it is used for high-bandwidth applications like Storage Area Networks (SANs).

Question 39

Why might a VPN or PPPoE connection require a smaller MTU size?

Answer 39

Because these protocols add extra encapsulation headers to the packets, which reduces the available space for the actual data payload within a standard-sized frame.

Question 40

What is a primary requirement for successfully implementing jumbo frames in a network?

Answer 40

All network devices in the communication path, including switches, routers, and network interface cards, must be configured to support the same jumbo frame size.