MAC addressing in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

📋 Factual

intermediate

What is the length of a MAC address?

A MAC address is a unique identifier assigned to network interfaces. How many bits long is a standard MAC address?

A 48 bits

B 32 bits

C 64 bits

D 128 bits

💡 Hint

Think about the common format shown as six groups of two hexadecimal digits.

A MAC address is 48 bits long, usually displayed as 6 pairs of hexadecimal digits (e.g., 00:1A:2B:3C:4D:5E).

🧠 Conceptual

intermediate

What does the first half of a MAC address represent?

A MAC address is split into two parts. What does the first 24 bits (first half) of a MAC address usually identify?

A The manufacturer or vendor

B The device's serial number

C The device's IP address

D The network subnet

💡 Hint

This part is assigned by a central authority to companies making network devices.

The first 24 bits of a MAC address are called the Organizationally Unique Identifier (OUI) and identify the manufacturer.

🔍 Analysis

advanced

Identify the error in this MAC address format

Which of the following MAC addresses is incorrectly formatted?

A 00:1A:2B:3C:4D:5E

B 00-1A-2B-3C-4D-5E

C 00:1A:2B:3C:4D:5G

D 001A.2B3C.4D5E

💡 Hint

Check if all characters are valid hexadecimal digits (0-9, A-F).

Option C contains '5G' where 'G' is not a valid hexadecimal digit, making it an invalid MAC address.

🚀 Application

advanced

How many unique MAC addresses can exist?

Given that a MAC address is 48 bits long, how many unique MAC addresses are possible?

A 2^32 (about 4 billion)

B 2^48 (about 281 trillion)

C 2^24 (about 16 million)

D 2^64 (about 18 quintillion)

💡 Hint

Calculate 2 raised to the power of the number of bits in a MAC address.

Since a MAC address is 48 bits, the total number of unique addresses is 2^48, approximately 281 trillion.

❓ Reasoning

expert

Why can't two devices on the same local network have the same MAC address?

Consider a local network where devices communicate using MAC addresses. What is the main reason two devices cannot share the same MAC address on this network?

A Because MAC addresses are used to route packets across the internet

B Because MAC addresses are encrypted for security and must be unique

C Because MAC addresses determine the device's IP address automatically

D Because MAC addresses uniquely identify devices on the local network to avoid communication conflicts

💡 Hint

Think about how devices find each other on the same network segment.

MAC addresses uniquely identify devices on a local network to ensure data is sent to the correct device without confusion or conflict.

Practice

1. What does a MAC address uniquely identify in a computer network?

easy

A. A network protocol type

B. An IP address on the internet

C. A website domain name

D. A device on a local network

Solution

1. Step 1: Understand the role of MAC addresses

   A MAC address is a unique identifier assigned to network interfaces for communications on the physical network segment.

2. Step 2: Identify what MAC addresses represent

   They identify devices on a local network, not IP addresses or domain names.

3. Final Answer:

   A device on a local network -> Option D

4. Quick Check:

   MAC address = device ID on local network [OK]

Hint: MAC addresses identify devices locally, not IPs or domains [OK]

Common Mistakes:

• Confusing MAC address with IP address
• Thinking MAC identifies websites
• Assuming MAC is a protocol

2. Which of the following is the correct format of a MAC address?

easy

A. 00:1A:2B:3C:4D:5E

B. 192.168.1.1

C. 255.255.255.0

D. http://192.168.1.1

Solution

1. Step 1: Recognize MAC address format

   MAC addresses are shown as six pairs of hexadecimal numbers separated by colons or dashes.

2. Step 2: Match the correct format

   00:1A:2B:3C:4D:5E matches this format: six pairs separated by colons with hex digits.

3. Final Answer:

   00:1A:2B:3C:4D:5E -> Option A

4. Quick Check:

   MAC format = hex pairs separated by colons [OK]

Hint: Look for six hex pairs separated by colons or dashes [OK]

Common Mistakes:

• Confusing MAC with IP address format
• Including URL or protocol parts
• Using decimal numbers instead of hex

3. Given the MAC address AC:DE:48:00:11:22, which part typically identifies the manufacturer?

medium

A. 00:11:22

B. 48:00:11

C. AC:DE:48

D. DE:48:00

Solution

1. Step 1: Understand MAC address structure

   The first three pairs (first 24 bits) of a MAC address identify the manufacturer, called the OUI (Organizationally Unique Identifier).

2. Step 2: Identify the first three pairs

   In AC:DE:48:00:11:22, the first three pairs are AC:DE:48, which represent the manufacturer.

3. Final Answer:

   AC:DE:48 -> Option C

4. Quick Check:

   First 3 pairs = manufacturer ID [OK]

Hint: First 3 hex pairs in MAC show manufacturer [OK]

Common Mistakes:

• Choosing last three pairs as manufacturer
• Mixing pairs in the middle
• Not knowing OUI meaning

4. A network admin sees a MAC address written as 00-1G-2B-3C-4D-5E. What is wrong with this MAC address?

medium

A. It is missing pairs

B. It has an invalid character 'G'

C. It uses colons instead of dashes

D. It has too many pairs

Solution

1. Step 1: Check valid characters in MAC address

   MAC addresses use hexadecimal digits: 0-9 and A-F only.

2. Step 2: Identify invalid character

   The character 'G' is not a valid hex digit, so the MAC address is invalid.

3. Final Answer:

   It has an invalid character 'G' -> Option B

4. Quick Check:

   Hex digits only: 0-9, A-F [OK]

Hint: MAC uses hex digits only; watch for invalid letters [OK]

Common Mistakes:

• Ignoring invalid hex characters
• Confusing dashes and colons as errors
• Counting pairs incorrectly

5. You want to filter a list of devices to only those from a specific manufacturer with OUI 00:1A:2B. Which method best uses MAC addresses to do this?

hard

A. Check if the MAC address starts with '00:1A:2B'

B. Check if the MAC address ends with '00:1A:2B'

C. Check if the MAC address contains '2B:00:1A'

D. Check if the MAC address has '00:1A:2B' anywhere in the middle

Solution

1. Step 1: Understand OUI position in MAC address

   The OUI is always the first three pairs of the MAC address, identifying the manufacturer.

2. Step 2: Choose the correct filtering method

   To filter devices by manufacturer, check if the MAC address starts with the OUI '00:1A:2B'.

3. Final Answer:

   Check if the MAC address starts with '00:1A:2B' -> Option A

4. Quick Check:

   OUI = start of MAC address [OK]

Hint: Filter by checking MAC start for OUI [OK]

Common Mistakes:

• Checking MAC end instead of start
• Looking for OUI in the middle
• Assuming OUI can be anywhere