📡 Paper 1 · 1.2 Communication and Internet Technologies
1.2.3 MAC Addresses, IP Addresses & Wireless Networking
Cambridge 9618 · International A Level Computer Science · ~15 min read
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MAC Addresses
A MAC (Media Access Control) address is a unique hardware identifier assigned to a Network Interface Card (NIC) by the manufacturer. It is used to identify devices on a local network (LAN).
48 bits long, written as 6 groups of 2 hexadecimal digits: e.g. A4:C3:F0:85:AC:2D
First 24 bits (OUI — Organisationally Unique Identifier) identify the manufacturer
Last 24 bits identify the specific device
Physically (burned) into the NIC — called a burned-in address (BIA)
Operates at the Data Link layer (Layer 2) of the OSI model
Used for communication within a LAN — switches use MAC addresses to forward frames
MAC addresses do not change as data crosses routers — routers use IP addresses for inter-network routing
IP Addresses
An IP (Internet Protocol) address is a logical address assigned to a device on a network. Unlike MAC addresses, IP addresses can change and are used for routing data across networks (the internet).
IPv4
32 bits long, written as 4 decimal octets separated by dots: e.g. 192.168.1.101
Gives ~4.3 billion unique addresses (2³²)
IPv4 address space is nearly exhausted — hence the move to IPv6
IPv6
128 bits long, written as 8 groups of 4 hexadecimal digits: e.g. 2001:0db8:85a3:0000:0000:8a2e:0370:7334
Also supports improved security and auto-configuration
Feature
IPv4
IPv6
Length
32 bits
128 bits
Notation
Decimal dotted (192.168.0.1)
Hexadecimal colon (2001:0db8::1)
Address space
~4.3 billion
~3.4 × 10³⁸
Header complexity
Variable, complex
Fixed, simpler
Security
IPsec optional
IPsec built-in
Static vs Dynamic IP Addresses
Static IP: manually assigned, permanently fixed — used for servers, printers, routers
Dynamic IP: assigned automatically by a DHCP server each time a device connects — common for client devices
Public vs Private IP Addresses
Public IP: globally unique, assigned by ISP — used to communicate over the internet
Private IP: used within a LAN (e.g. 192.168.x.x, 10.x.x.x) — not routable on the internet
NAT (Network Address Translation) allows many devices with private IPs to share one public IP
Wireless Networking (Wi-Fi)
Wireless LANs use radio waves to transmit data. The main standard is IEEE 802.11 (Wi-Fi).
Key components
Wireless Access Point (WAP): a device that allows wireless devices to connect to a wired network — functions as a bridge between wireless and wired segments
SSID (Service Set Identifier): the network name broadcast by the WAP so devices can identify it
NIC with wireless adapter: required in the client device
Wireless Security
Protocol
Security level
Notes
WEP
Very weak
Easily cracked — obsolete
WPA
Moderate
Improved over WEP but vulnerabilities exist
WPA2
Strong
Uses AES encryption — current standard
WPA3
Very strong
Newest standard — better protection against brute-force
Wireless Channels and Interference
Wireless networks operate on radio frequency bands (2.4 GHz and 5 GHz). Multiple overlapping networks on the same channel cause interference, reducing performance. Using different channels reduces interference.
Exam tip: Cambridge often asks to compare MAC vs IP addresses. Key points: MAC = hardware/physical/Layer 2/48-bit/hex/NIC manufacturer/LAN only. IP = logical/Layer 3/32-bit(v4) or 128-bit(v6)/decimal(v4) or hex(v6)/changes across networks. Also know: IPv4 vs IPv6 differences, static vs dynamic, public vs private, and the role of DHCP.
⚠️ Common Mistakes
Saying MAC addresses change — they are burned in and permanent (though software can spoof them)
Saying IP addresses are used within a LAN for frame delivery — MAC addresses handle this on a LAN; IP is used for inter-network routing
Confusing SSID with a password — SSID is the network name, not the password
8 questions · instantly marked · Cambridge 9618 standard
Q1State three differences between a MAC address and an IP address.[3]
✅ Mark scheme
Mark scheme
One mark each for any three: MAC is a hardware/physical address burned into the NIC; IP is a logical/software address [1]; MAC is 48 bits; IPv4 is 32 bits / IPv6 128 bits [1]; MAC uses hexadecimal; IPv4 uses dotted decimal [1]; MAC only used within a LAN; IP used for routing across networks (internet) [1]; MAC doesn't change; IP can change (dynamic/DHCP) [1].
Q2Explain what the first 24 bits of a MAC address represent.[2]
✅ Mark scheme
Mark scheme
The first 24 bits are the OUI (Organisationally Unique Identifier) [1]; they identify the manufacturer/vendor of the NIC [1].
Q3Explain why IPv6 was developed to replace IPv4.[3]
✅ Mark scheme
Mark scheme
IPv4 only provides ~4.3 billion addresses (2³²) [1]; this address space is nearly exhausted due to the explosive growth of internet-connected devices [1]; IPv6 provides 2¹²⁸ ≈ 3.4 × 10³⁸ addresses — sufficient for the foreseeable future [1].
Q4Distinguish between a static IP address and a dynamic IP address. State a suitable use for each.[4]
✅ Mark scheme
Mark scheme
Static: a fixed IP address manually assigned; suitable for servers, printers, or routers where the address must remain the same [2]; Dynamic: an IP address automatically assigned by DHCP each time a device connects; suitable for client devices such as laptops or smartphones [2].
Q5Explain the purpose of NAT (Network Address Translation) in a home network.[3]
✅ Mark scheme
Mark scheme
NAT allows multiple devices on a home network to share a single public IP address [1]; each device is assigned a private IP address on the LAN; when traffic leaves the network, the router translates private IPs to the single public IP [1]; this conserves IPv4 address space and also adds a degree of security by hiding internal IP addresses [1].
Q6State the purpose of an SSID in a wireless network.[2]
✅ Mark scheme
Mark scheme
SSID (Service Set Identifier) is the name of the wireless network [1]; it is broadcast by the WAP so that devices in range can identify and connect to the correct network [1].
Q7Compare WEP and WPA2 as wireless security protocols.[4]
✅ Mark scheme
Mark scheme
WEP (Wired Equivalent Privacy) is an older, very weak protocol — it uses a static key that can be cracked quickly [1]; it is now considered obsolete and should not be used [1]; WPA2 uses AES (Advanced Encryption Standard) encryption with dynamic key exchange [1]; it is currently the standard for secure Wi-Fi — much harder to crack than WEP [1].
Q8A company has 300 employees all connecting to the internet through one router. Explain how this is possible using public and private IP addresses.[3]
✅ Mark scheme
Mark scheme
Each device on the company's LAN is assigned a private IP address (e.g. 192.168.x.x) [1]; the company router has a single public IP address assigned by the ISP [1]; NAT on the router translates outgoing private IP addresses to the public IP address — allowing all devices to share the one public address for internet communication [1].
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Mini Test — 1.2.3 MAC, IP & Wireless
10 questions · 10 marks · 10 minutes
⏱ 10:00
10 marks
Section A — Multiple Choice [5 marks]
Q1How many bits is a MAC address?
Q2IPv6 addresses are how many bits long?
Q3What does DHCP do?
Q4Which wireless security protocol is considered current standard?
Q5A MAC address is used for communication:
Section B — Short Answer [5 marks]
Q6State one reason why IPv6 was developed to replace IPv4.
Mark schemeIPv4 address space (~4.3 billion) is nearly exhausted; IPv6 provides 2¹²⁸ addresses — sufficient for all current and future internet-connected devices [1 mark].
Q7State what OUI stands for and what it identifies in a MAC address.
Mark schemeOUI = Organisationally Unique Identifier [1]; identifies the manufacturer/vendor of the NIC [1]. [1 mark for either point].
Q8Explain what NAT (Network Address Translation) does.
Mark schemeNAT translates private IP addresses (used on a LAN) to a single public IP address when communicating with the internet, allowing multiple devices to share one public IP [1 mark].
Q9State the purpose of an SSID in a wireless network.
Mark schemeSSID is the name of the wireless network broadcast by the WAP so that devices can identify and connect to the correct network [1 mark].
Q10State one difference between a static and a dynamic IP address.
Mark schemeA static IP address is permanently fixed/manually assigned; a dynamic IP is automatically assigned by DHCP and can change each time the device connects [1 mark].