MAC addressing in Computer Networks - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does MAC stand for in MAC addressing?

MAC stands for Media Access Control. It is a unique identifier assigned to network interfaces for communications on the physical network segment.

beginner

How many bytes long is a MAC address?

A MAC address is 6 bytes (48 bits) long. It is usually shown as 12 hexadecimal digits.

beginner

What is the typical format of a MAC address?

A MAC address is typically written as six groups of two hexadecimal digits, separated by colons (:) or hyphens (-), for example: 00:1A:2B:3C:4D:5E.

intermediate

Who assigns the first half of a MAC address and what does it represent?

The first half (first 3 bytes) of a MAC address is assigned by the IEEE to manufacturers and is called the Organizationally Unique Identifier (OUI). It identifies the device maker.

intermediate

Can MAC addresses be changed by users?

MAC addresses are usually fixed by the manufacturer, but some devices and software allow users to change or 'spoof' the MAC address temporarily.

What is the length of a MAC address?

A 48 bits

B 32 bits

C 64 bits

D 128 bits

A MAC address is 48 bits long, which equals 6 bytes.

Which part of the MAC address identifies the manufacturer?

A First 3 bytes

B Last 3 bytes

C Middle 2 bytes

D Entire 6 bytes

The first 3 bytes of a MAC address are the Organizationally Unique Identifier (OUI) assigned to manufacturers.

Which of the following is a valid MAC address format?

A 192.168.1.1

B 255.255.255.0

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

D http://example.com

MAC addresses are shown as six groups of two hexadecimal digits separated by colons or hyphens.

Can MAC addresses be changed by users?

A Yes, always

B Sometimes, with special software

C No, they are permanently fixed

D Only by the manufacturer

Users can sometimes change or spoof MAC addresses using special software or device settings.

What does MAC addressing help with in a network?

A Routing internet traffic

B Assigning IP addresses

C Encrypting data

D Identifying devices on the local network

MAC addresses uniquely identify devices on the local network segment for communication.

Explain what a MAC address is and why it is important in networking.

Think about how devices recognize each other on the same network.

Describe the structure of a MAC address and the role of the Organizationally Unique Identifier (OUI).

Consider how the address shows who made the device and which device it is.

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