← IGCSE Computer Science Paper 1

Manufacturer code and serial code in a MAC address

First 3 pairs (00:1A:2B) are the manufacturer code; last 3 pairs (3C:4D:5E) are the serial code that makes this NIC unique.

Part of: IGCSE Computer Science 0478 — 3.4 Network Hardware — Module 9

Understanding Manufacturer code and serial code in a MAC address in IGCSE Computer Science Paper 1

What it does: Both addresses start with 00:1A:2B, so the same company made them. The serial codes 3C:4D:5E and 7F:8A:9B differ, so each NIC is unique. The six pairs divide into the first three (manufacturer code) and the last three (serial code). A different manufacturer code means a different company made the NIC.

Common mistakes: A MAC address has six pairs. This one only has five, so the serial code is incomplete. It should be "00:1A:2B:3C:4D:5E". The label says Serial, so it must output the serial variable (the last three pairs), not the manufacturer code. It should be OUTPUT "Serial: " + serial.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 325–341) and word search (Modules 325–354).

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Learning
Duo
In the MAC address 00:1A:2B:3C:4D:5E, which part is the manufacturer code?
3C:4D:5E (the last three pairs)00:1A:2B (the first three pairs)
Matches
00:1A:2B:3C:4D:5E - the serial code is 00:1A:2B
↓
00:1A:2B is the first half, so it is the manufacturer code, not the serial code. The serial code is the last half, 3C:4D:5E.
Applying
Meanings
Term
00:1A:2B:3C:4D:5E
Meaning
First 3 pairs (00:1A:2B) are the manufacturer code; last 3 pairs (3C:4D:5E) are the serial code that makes this NIC unique.
Practice
MAC ← "00:1A:2B:3C:4D:5E"
Testing
Gaps
Manufacturer code:
Check Answer
Spots
1mac ← "00:1A:2B:3C:4D:5E"
2mac ← "00:1A:2B:3C:4D"

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Quick Questions

1. In the MAC address 00:1A:2B:3C:4D:5E, which part is the manufacturer code?
A. 00:1A:2B (the first three pairs) ✓
B. 3C:4D:5E (the last three pairs)
The first half (first three pairs) identifies the company that made the NIC. The second half is the serial code.
2. In the MAC address 00:1A:2B:3C:4D:5E, which part is the serial code?
A. 00:1A:2B (the first three pairs)
B. 3C:4D:5E (the last three pairs) ✓
The last three pairs are the serial code, which the manufacturer gives to each NIC it makes.
3. Two NICs are made by the same manufacturer. What is true about their MAC addresses?
A. They have the same second half
B. They have the same first half ✓
The same manufacturer uses the same manufacturer code, so the first three pairs match. The serial codes must differ.
4. Why do two NICs from the same manufacturer have different serial codes?
A. So that each NIC has a unique MAC address ✓
B. So that the manufacturer can be identified
The serial code makes each NIC unique. The manufacturer code is what identifies the company.
5. A NIC has the MAC address A4:5E:60:11:22:33. Another NIC has A4:5E:60:99:88:77. What does this show?
A. Same manufacturer, different serial codes ✓
B. Different manufacturers, same serial code
Both start with A4:5E:60, so the manufacturer is the same. The last three pairs differ, so each NIC is unique.

Match the Pairs

00:1A:2B → The first half of the MAC address 00:1A:2B:3C:4D:5E, which is the manufacturer code
3C:4D:5E → The second half of the MAC address 00:1A:2B:3C:4D:5E, which is the serial code that makes this NIC unique
Two NICs made by the same manufacturer share the same first half but have different second halves → 00:1A:2B:3C:4D:5E and 00:1A:2B:7F:8A:9B
A MAC address is split into two halves of three pairs each: manufacturer code, then serial code → 00:1A:2B | 3C:4D:5E
00:1A:2B:3C:4D:5E - the serial code is 00:1A:2B → 00:1A:2B is the first half, so it is the manufacturer code, not the serial code. The serial code is the last half, 3C:4D:5E.
Two NICs from the same manufacturer have the same serial code → Two NICs from the same manufacturer share the manufacturer code, but each has a different serial code so that every NIC is unique.

Key Term

00:1A:2B:3C:4D:5E
First 3 pairs (00:1A:2B) are the manufacturer code; last 3 pairs (3C:4D:5E) are the serial code that makes this NIC unique.

Fill in the Blanks

1. MAC address: 00:1A:2B:3C:4D:5E Manufacturer code: 00:1A:2B
Hint: Type the first three pairs of the MAC address, which identify the manufacturer.
2. MAC address: 00:1A:2B:3C:4D:5E Serial code: 3C:4D:5E
Hint: Type the last three pairs of the MAC address, which make this NIC unique.
3. NIC 1: 00:1A:2B:3C:4D:5E NIC 2 (same maker): 00:1A:2B:7F:80:91
Hint: Both NICs come from the same manufacturer. Type the first half they must share.
4. NIC 1: 00:1A:2B:3C:4D:5E NIC 2: 00:1A:2B:7F:80:91 Serial codes are different for each NIC
Hint: Type the word that describes how the serial codes of two NICs compare.
5. First 3 pairs = manufacturer code Last 3 pairs = serial code
Hint: Type the name of the code in the second half that makes each NIC unique.

Spot the Error

Question 1
A mac ← "00:1A:2B:3C:4D:5E"
B mac ← "00:1A:2B:3C:4D"
C serial ← "3C:4D:5E"
Line B — A MAC address has six pairs. This one only has five, so the serial code is incomplete. It should be "00:1A:2B:3C:4D:5E".
Question 2
A mac ← "00:1A:2B:3C:4D:5E"
B maker ← "00:1A:2B"
C serial ← "3C:4D:5E"
D OUTPUT "Serial: " + maker
Line D — The label says Serial, so it must output the serial variable (the last three pairs), not the manufacturer code. It should be OUTPUT "Serial: " + serial.
Question 3
A DECLARE mac : INTEGER
B mac ← "00:1A:2B:3C:4D:5E"
C OUTPUT mac
Line A — A MAC address contains colons and hexadecimal letters such as A to F, so it must be stored as text. It should be DECLARE mac : STRING.
Question 4
A nic1 ← "00:1A:2B:3C:4D:5E"
B nic2 ← "00:1A:2B:7F:80:91"
C sameMaker ← FALSE
D sameSerial ← FALSE
Line C — Both NICs start with 00:1A:2B, so they have the same manufacturer code. sameMaker should be TRUE.
Question 5
A mac ← "00:1A:2B:3C:4D:5E"
B maker ← LEFT(mac, 8)
C serial ← RIGHT(mac, 8)
D OUTPUT "NIC id: " + maker
Line D — The serial code is what makes this NIC unique, because many NICs share a manufacturer code. It should output serial, not maker.

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