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Network addressing: IPv4, IPv6 and MAC addresses

Edexcel IAL Computer Science · WCP01 Principles of Computer Science

Every device on a network needs addresses so data can be delivered. IP addresses identify a device's location on a network; MAC addresses identify its network hardware (spec point 3.1.3).

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IPv4

An IPv4 address is 32 bits, written as four denary numbers (each 8 bits, 0 to 255) separated by dots, for example 192.168.1.25.
In binary: 11000000.10101000.00000001.00011001.
Number of possible addresses = 2³² = 4 294 967 296, about 4.3 billion. This is not enough for every device on the internet, which is why IPv6 was introduced (along with private addresses behind a router).

IPv6

An IPv6 address is 128 bits, written as eight groups of four hexadecimal digits separated by colons, for example 2001:0db8:0000:0000:0000:ff00:0042:8329.
Leading zeros in a group can be dropped, and one run of all-zero groups can be replaced by :: (only once), giving 2001:db8::ff00:42:8329.
Number of possible addresses = 2¹²⁸, about 3.4 x 10³⁸, so the address space will not run out.
Each group of 4 hex digits = 16 bits, and 8 x 16 = 128.

MAC addresses and how they work together

A MAC (media access control) address is a 48-bit address given to a network interface card when it is made. It is written as six pairs of hex digits, for example 3C:5A:B4:12:9F:0E. It is normally fixed and unique worldwide; the first half identifies the manufacturer.
IP addresses are logical and can change (assigned by the network, often by DHCP); they are used by routers to send packets across networks. MAC addresses are physical and used by switches to deliver frames to the right device within the local network.
Expressions: n bits give 2ⁿ addresses; a 48-bit MAC space has 2⁴⁸ addresses.

Worked example

Convert the IPv4 address 192.168.1.25 to binary.

192 = 11000000
168 = 10101000
1 = 00000001
25 = 00011001

Answer: 11000000.10101000.00000001.00011001

Key idea: IPv4: 32 bits, four denary octets, 2³² addresses. IPv6: 128 bits, eight groups of 4 hex digits, 2¹²⁸. MAC: 48 bits, six hex pairs, fixed to the NIC; routers use IP, switches use MAC.

Check yourself

How many bits are in an IPv4 address?
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32. Four 8-bit numbers: 4 x 8 = 32.
What is the largest number that can appear in one part of an IPv4 address?
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255. Each part is 8 bits: 2⁸ - 1 = 255.
An IPv6 address has 8 groups of 4 hexadecimal digits. How many bits does each group hold?
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16. Each hex digit is 4 bits, so 4 x 4 = 16 bits.
Convert the IPv4 part 172 to 8-bit binary.
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10101100. 172 = 128 + 32 + 8 + 4 = 10101100.
An IPv4 octet is 11000000 in binary. What is it in denary?
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192. 128 + 64 = 192.
Which statement about MAC addresses is correct?
- They are 32-bit addresses assigned by the router
- They change every time a device joins a network
- They are used by routers to send data across the internet
- They are 48-bit addresses assigned to a network interface card when it is made
Show answer
They are 48-bit addresses assigned to a network interface card when it is made. MAC addresses are physical, fixed and used within a local network.
Which is a valid IPv4 address?
- 10.0.256.17
- 10.0.255.17
- 10.0.17
- 10:0:255:17
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10.0.255.17. Four parts, each 0 to 255, separated by dots.
Explain why IPv6 was introduced.
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IPv4 uses 32 bits so it has only about 4.3 billion addresses, which is not enough for all the devices connected to the internet; IPv6 uses 128 bits giving a vastly larger number of addresses.. Compare the size of the address spaces.

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Sources

Pearson Edexcel International Advanced Subsidiary/Advanced Level in Computer Science specification (2026)

Last updated 8 November 2026. Spotted a mistake? Tell us.