← IGCSE Computer Science Paper 1

MAC address format

A MAC address is six pairs of hex digits (two digits per pair, 48 bits in total), separated by colons or hyphens, such as 00:1A:2B:3C:4D:5E.

Part of: IGCSE Computer Science 0478 — 3.4 Network Hardware — Module 8, ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 15, WA Computer Science ATAR Year 11 — Network Communications — Module 36

Understanding MAC address format in IGCSE Computer Science Paper 1

What it does: 3C is one pair of two hex digits. A MAC address is made of six pairs like this, and each pair is 8 bits. MAC addresses are written with colons or hyphens between the pairs. Full stops are used in IPv4 addresses. The wrong option has seven pairs. A MAC address must have exactly six pairs, whichever separator is used. Hex digits only run from 0 to 9 and A to F. G is not a hex digit, so G7 cannot appear in a MAC address. A MAC address has six pairs. Four numbers is the format of an IPv4 address.

Common mistakes: This MAC address uses colons as separators, so it must be split on ":". Splitting on "-" would leave the whole address as one piece. It should be pairs = mac.split(":"). A MAC address has six pairs of hex digits, not eight. It should be pairs = 6, which gives 12 hex digits in total.

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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

Which is a correctly formatted MAC address?

00:1A:2B:3C:4D00:1A:2B:3C:4D:5E

Matches

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

↓

Only five pairs are shown. A MAC address needs six pairs of hex digits (48 bits), so one pair is missing.

Applying

Meanings

Term

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

Meaning

A MAC address is six pairs of hex digits (two digits per pair, 48 bits in total), separated by colons or hyphens, such as 00:1A:2B:3C:4D:5E.

Practice

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

Testing

Gaps

A MAC address has pairs of hex digits.

Check Answer

Spots

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

2pairs = mac.split("-")

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Quick Questions

1. Which is a correctly formatted MAC address?

A. 00:1A:2B:3C:4D:5E ✓

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

A MAC address has six pairs of hex digits. The wrong option has only five pairs.

2. How many bits are in a MAC address?

A. 32 bits

B. 48 bits ✓

Six pairs of hex digits is 12 hex digits. Each hex digit is 4 bits, so 12 x 4 = 48 bits. 32 bits is the size of an IPv4 address.

3. How many hex digits are in each pair of a MAC address?

A. Two hex digits per pair ✓

B. Three hex digits per pair

Each pair has exactly two hex digits. Two hex digits make 8 bits, which is one byte.

4. Which separators can be used in a MAC address?

A. Colons (:) or hyphens (-) ✓

B. Full stops (.) or colons (:)

MAC addresses are written with colons or hyphens between the pairs. Full stops are used in IPv4 addresses.

5. Which MAC address is written correctly using hyphens?

A. 00-1A-2B-3C-4D-5E-6F

B. 00-1A-2B-3C-4D-5E ✓

The wrong option has seven pairs. A MAC address must have exactly six pairs, whichever separator is used.

Match the Pairs

00:1A:2B:3C:4D:5E → A MAC address written as six pairs of hex digits separated by colons

00-1A-2B-3C-4D-5E → The same kind of MAC address written with hyphens as separators instead of colons

Each pair in a MAC address is two hex digits, so it can range from 00 to FF → 3C

A MAC address has six pairs of two hex digits, which is 6 x 8 = 48 bits in total → A4:5E:60:D2:19:7B

00:1A:2B:3C:4D → Only five pairs are shown. A MAC address needs six pairs of hex digits (48 bits), so one pair is missing.

00:1A:2B:3C:4D:5G → G is not a hex digit. Hex digits are only 0 to 9 and A to F, so the last pair is invalid.

Key Term

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

A MAC address is six pairs of hex digits (two digits per pair, 48 bits in total), separated by colons or hyphens, such as 00:1A:2B:3C:4D:5E.

Fill in the Blanks

1. A MAC address has 6 pairs of hex digits.

Hint: Type how many pairs of hex digits make up a MAC address.

2. Each pair in a MAC address has 2 hex digits.

Hint: Type the number of hex digits in each pair.

3. A MAC address is 48 bits in total.

Hint: Type the total number of bits in a MAC address.

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

Hint: Type the separator that matches the others in this MAC address (colons or hyphens are both allowed, but not mixed).

5. 6 pairs x 8 bits per pair = 48 bits

Hint: Type the number of bits in one pair of hex digits (each hex digit is 4 bits).

Spot the Error

Question 1

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

B pairs = mac.split("-")

C print(len(pairs))

Line B — This MAC address uses colons as separators, so it must be split on ":". Splitting on "-" would leave the whole address as one piece. It should be pairs = mac.split(":").

Question 2

A pairs = 8

B per_pair = 2

C total = pairs * per_pair

D print(total)

Line A — A MAC address has six pairs of hex digits, not eight. It should be pairs = 6, which gives 12 hex digits in total.

Question 3

A pairs = 6

B digits = pairs * 2

C bits = digits * 4

D print("Bits:", digits)

Line D — The program should print the number of bits (48), not the number of hex digits (12). It should be print("Bits:", bits).

Question 4

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

B ok = len(mac) == 12

C print(ok)

Line B — The text has 12 hex digits plus 5 hyphen separators, so its length is 17, not 12. It should be ok = len(mac) == 17.

Question 5

A mac = "A4-C3-F0-85-12"

B parts = mac.split("-")

C print(parts[0])

Line A — This MAC address has only five pairs. A valid MAC address needs six pairs of hex digits, so a sixth pair such as -9B is missing.

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