Ethernet protocol basics in Computer Networks - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Ethernet?

Ethernet is a common technology used to connect devices in a local area network (LAN). It allows devices to communicate by sending data packets over cables.

beginner

What type of cable is commonly used in Ethernet connections?

Twisted pair cables, especially Cat5e or Cat6 cables, are commonly used for Ethernet connections. They help reduce interference and allow fast data transfer.

beginner

What is the role of MAC addresses in Ethernet?

MAC addresses are unique identifiers assigned to each network device. Ethernet uses MAC addresses to know where to send data packets within the local network.

intermediate

How does Ethernet handle data collisions?

Ethernet uses a method called CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to detect when two devices send data at the same time and then waits before retrying.

beginner

What speeds can Ethernet support?

Ethernet supports various speeds including 10 Mbps, 100 Mbps (Fast Ethernet), 1 Gbps (Gigabit Ethernet), and even 10 Gbps or higher in modern networks.

What does Ethernet primarily connect?

A Devices in a local area network

B Web servers on the internet

C Mobile phones to satellites

D Printers to paper

Ethernet is mainly used to connect devices within a local area network (LAN).

Which cable type is most commonly used for Ethernet?

A USB cable

B Coaxial cable

C Twisted pair cable

D Fiber optic cable

Twisted pair cables like Cat5e or Cat6 are the most common for Ethernet connections.

What does a MAC address do in Ethernet?

A Encrypts data packets

B Identifies a device uniquely on the network

C Measures cable length

D Controls internet speed

MAC addresses uniquely identify devices so Ethernet knows where to send data.

What is CSMA/CD used for in Ethernet?

A Encrypting data

B Increasing cable length

C Assigning IP addresses

D Detecting and managing data collisions

CSMA/CD helps Ethernet detect when two devices send data simultaneously and manage collisions.

Which of these is NOT a common Ethernet speed?

A 100 Gbps

B 1 Gbps

C 10 Gbps

D 100 Mbps

While 100 Gbps Ethernet exists, it is not common in basic Ethernet networks; typical speeds are up to 10 Gbps.

Explain how Ethernet devices use MAC addresses to communicate within a network.

Think about how devices know where to send data.

Describe the purpose of CSMA/CD in Ethernet and how it helps manage data transmission.

Consider what happens when two devices send data at the same time.

Practice

1. What is the primary purpose of the Ethernet protocol in computer networks?

easy

A. To define how devices communicate over a local area network

B. To assign IP addresses to devices

C. To encrypt data sent over the internet

D. To manage wireless connections

Solution

1. Step 1: Understand Ethernet's role

   Ethernet is a protocol used mainly for communication within local area networks (LANs).

2. Step 2: Compare with other network functions

   Assigning IP addresses is done by DHCP, encryption by security protocols, and wireless management by Wi-Fi standards.

3. Final Answer:

   To define how devices communicate over a local area network -> Option A

4. Quick Check:

   Ethernet = LAN communication [OK]

Hint: Ethernet is about local network communication [OK]

Common Mistakes:

• Confusing Ethernet with IP address assignment
• Thinking Ethernet manages wireless connections
• Assuming Ethernet encrypts data

2. Which part of an Ethernet frame contains the unique hardware address of the sending device?

easy

A. Payload

B. Destination IP address

C. Frame Check Sequence

D. Source MAC address

Solution

1. Step 1: Identify frame components

   An Ethernet frame includes source and destination MAC addresses, payload, and error-checking fields.

2. Step 2: Locate the sender's hardware address

   The source MAC address field holds the unique hardware address of the sending device.

3. Final Answer:

   Source MAC address -> Option D

4. Quick Check:

   Sender's hardware = Source MAC address [OK]

Hint: Source MAC = sender's hardware address [OK]

Common Mistakes:

• Confusing payload with address fields
• Mixing IP address with MAC address
• Thinking Frame Check Sequence holds addresses

3. Consider this simplified Ethernet frame structure:
Destination MAC | Source MAC | Type | Payload | CRC
Which part is responsible for detecting errors in the frame?

medium

A. Type

B. Payload

C. CRC

D. Source MAC

Solution

1. Step 1: Understand frame fields

   The CRC (Cyclic Redundancy Check) field is used to detect errors in the frame data.

2. Step 2: Differentiate other fields

   Type indicates the protocol, Payload carries data, and Source MAC is the sender's address, none detect errors.

3. Final Answer:

   CRC -> Option C

4. Quick Check:

   Error detection = CRC [OK]

Hint: CRC checks for errors in Ethernet frames [OK]

Common Mistakes:

• Confusing Type field with error detection
• Assuming Payload includes error checking
• Mixing Source MAC with error detection

4. A network technician notices that Ethernet frames are being dropped due to collisions. Which Ethernet feature helps to reduce collisions in a shared network?

medium

A. MAC Address Filtering

B. Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

C. IP Addressing

D. Encryption

Solution

1. Step 1: Identify collision handling method

   CSMA/CD is the Ethernet protocol feature that listens before sending and detects collisions to reduce frame loss.

2. Step 2: Eliminate unrelated options

   IP addressing manages network layer routing, MAC filtering controls access, and encryption secures data, none reduce collisions.

3. Final Answer:

   Carrier Sense Multiple Access with Collision Detection (CSMA/CD) -> Option B

4. Quick Check:

   Collision reduction = CSMA/CD [OK]

Hint: CSMA/CD manages collisions in Ethernet [OK]

Common Mistakes:

• Confusing IP addressing with collision control
• Thinking MAC filtering prevents collisions
• Assuming encryption affects collisions

5. You want to design a network where devices communicate using Ethernet frames but avoid collisions entirely. Which modern Ethernet technology should you choose?

hard

A. Full-duplex Ethernet with switches

B. Half-duplex Ethernet with hubs

C. Wireless Ethernet with CSMA/CA

D. Token Ring Ethernet

Solution

1. Step 1: Understand collision domains

   Half-duplex Ethernet with hubs shares the medium, causing collisions; full-duplex with switches separates devices.

2. Step 2: Evaluate options for collision avoidance

   Full-duplex Ethernet with switches allows simultaneous send/receive without collisions. Wireless uses CSMA/CA, not Ethernet. Token Ring is a different protocol.

3. Final Answer:

   Full-duplex Ethernet with switches -> Option A

4. Quick Check:

   No collisions = Full-duplex + switches [OK]

Hint: Switches + full-duplex avoid Ethernet collisions [OK]

Common Mistakes:

• Choosing hubs which cause collisions
• Confusing wireless CSMA/CA with Ethernet collision control
• Thinking Token Ring is Ethernet