← IGCSE Computer Science Paper 1

IP addresses are allocated by the network

A device is given its IP address by the network it joins, not by the manufacturer, so it can change on a new network. Unlike a MAC address, it is not built into the NIC.

Part of: IGCSE Computer Science 0478 — 3.4 Network Hardware — Module 13

Understanding IP addresses are allocated by the network in IGCSE Computer Science Paper 1

What it does: The router on the network allocates the IP address when the phone joins, so the address does not come from the manufacturer. The tablet's NIC is the same in both places, but each network gave a different IP address. The MAC address is set at manufacture and stored in the NIC. The IP address is not built in. An IP address depends on the network, so it can change. A MAC address is the one fixed to the hardware. Students often mix up the MAC address (set at manufacture) with the IP address (allocated by the network).

Common mistakes: An IP address is not built into the NIC. The network the laptop joins assigns it, so it should be network.assign(). The manufacturer does not give out IP addresses. The network the phone joins allocates its IP, so it should be network.assign().

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Learning
Duo
Who gives a device its IP address?
The network the device joinsThe manufacturer of the device
Matches
The manufacturer sets the IP address of a device when it is made.
↓
Wrong: the manufacturer gives the MAC address, not the IP address. The network the device joins allocates the IP address.
Applying
Meanings
Term
IP address allocation
Meaning
A device is given its IP address by the network it joins, not by the manufacturer, so it can change on a new network. Unlike a MAC address, it is not built into the NIC.
Practice
mac ← "00:1A:2B:3C:4D:5E"
Testing
Gaps
device.ipAddress ← .allocate()
Check Answer
Spots
2network ← join("SchoolWiFi")
3laptop.ip ← nic.factoryIP()

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Quick Questions

1. Who gives a device its IP address?
A. The manufacturer of the device
B. The network the device joins ✓
An IP address is allocated by the network. The manufacturer sets the MAC address, not the IP address.
2. A laptop moves from a school network to a home network. What happens to its IP address?
A. It is likely to change to a new one ✓
B. It stays exactly the same
Each network allocates its own IP addresses, so a new network gives the device a new IP address.
3. Which address is built into the NIC when it is made?
A. MAC address ✓
B. IP address
The MAC address is set at manufacture and stored in the NIC. The IP address is not built in.
4. True or false: an IP address is set by the manufacturer at the factory.
A. True
B. False ✓
The network allocates the IP address when the device joins. Only the MAC address is given at manufacture.
5. Which statement about IP addresses is correct?
A. It depends on the network the device is connected to ✓
B. It is permanently fixed to the device's hardware
An IP address depends on the network, so it can change. A MAC address is the one fixed to the hardware.

Match the Pairs

Laptop at home: 192.168.1.20 -> Laptop at school: 10.0.5.47 → The same device gets a different IP address on a new network, because the network allocates the address.
MAC address: 00:1A:2B:3C:4D:5E (stays the same on every network) → An address built into the NIC at manufacture, so unlike an IP address it does not change when the device joins a new network.
An IP address is given to a device by the network it joins, not by the manufacturer. → Phone joins Wi-Fi -> Router gives IP 192.168.0.12
An IP address is not built into the NIC, so it can change when the device moves to another network. → Tablet on café Wi-Fi: 172.16.4.9 / Tablet on home Wi-Fi: 192.168.1.8
The manufacturer sets the IP address of a device when it is made. → Wrong: the manufacturer gives the MAC address, not the IP address. The network the device joins allocates the IP address.
A device keeps the same IP address on every network because it is built into the NIC. → Wrong: the IP address is not built into the NIC. It depends on the network and changes when the device joins a new network.

Key Term

IP address allocation
A device is given its IP address by the network it joins, not by the manufacturer, so it can change on a new network. Unlike a MAC address, it is not built into the NIC.

Fill in the Blanks

1. nic.macAddress ← manufacturer.assign() device.ipAddress ← network.allocate()
Hint: Type the name of what gives a device its IP address when it joins.
2. IF newNetwork <> oldNetwork THEN device.ipAddress ← newNetwork.allocate() ENDIF
Hint: Type the operator that means not equal to.
3. joinNetwork(device, network) device.ipAddress ← network.allocate() OUTPUT device.ipAddress
Hint: Type the method name the network uses to give out an IP address.
4. IF device.joinsNewNetwork THEN device.ipAddress ← network.allocate() ENDIF
Hint: Type the keyword that follows an IF condition.
5. nic.macAddress ← manufacturer.assign() device.ipAddress ← network.allocate()
Hint: Type the property that the network sets and that can change.

Spot the Error

Question 1
A laptop.mac ← nic.mac
B network ← join("SchoolWiFi")
C laptop.ip ← nic.factoryIP()
Line C — An IP address is not built into the NIC. The network the laptop joins assigns it, so it should be network.assign().
Question 2
A phone.ip ← maker.assign()
B OUTPUT phone.ip
C phone.mac ← nic.mac
Line A — The manufacturer does not give out IP addresses. The network the phone joins allocates its IP, so it should be network.assign().
Question 3
A IF sameNetwork THEN
B device.ip ← network.assign()
C ENDIF
Line A — A new IP address is allocated when the device joins a new network. The condition should be joinsNewNetwork, not sameNetwork.
Question 4
A home.ip ← homeNet.assign()
B cafe.ip ← home.ip
C OUTPUT home.ip, cafe.ip
Line B — The cafe network gives the device its own IP address. It does not reuse the home one. It should be cafe.ip ← cafeNet.assign().
Question 5
A nic.mac ← "A4:5E:60:C1:09:7B"
B ip ← network.assign()
C OUTPUT "IP never changes"
Line C — The MAC address is built into the NIC and stays the same. The IP address depends on the network and can change. The output should say MAC never changes.

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