← IGCSE Computer Science Paper 1

Dynamic IP address

An IP address given to a device automatically by the network each time it connects, so it may change and can later be reused by another device.

Part of: IGCSE Computer Science 0478 — 3.4 Network Hardware — Module 21, ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 21, WA Computer Science ATAR Year 11 — Network Communications — Module 44

Understanding Dynamic IP address in IGCSE Computer Science Paper 1

What it does: When a device disconnects, its dynamic address goes back to the pool, so the network can give the same address to a different device. Being able to change is the key feature of a dynamic IP address. A fixed address is called a static IP address.

Common mistakes: A dynamic IP address is assigned automatically by the network, not set manually. The line should say the address is automatic. With a dynamic IP address the network assigns a new address each time the device connects, so it may differ. ip2 should be ip2 <- network.ASSIGN(), not a copy of ip1.

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This module's key terms are also in a printable crossword (Modules 342–354) and word search (Modules 325–354).

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Learning
Duo
Who or what gives a device a dynamic IP address?
The network assigns it automaticallyThe user types it in by hand every time
Matches
A dynamic IP address never changes, so it is the same every time you connect.
↓
Wrong: a dynamic IP address may change each time the device connects. An address that never changes is a static IP address.
Applying
Meanings
Term
dynamic IP address
Meaning
An IP address given to a device automatically by the network each time it connects, so it may change and can later be reused by another device.
Practice
WHEN device connects
Testing
Gaps
ip ← network.(device)
Check Answer
Spots
3address <- network.ASSIGN()
4OUTPUT "Address is manual"

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Quick Questions

1. Who or what gives a device a dynamic IP address?
A. The network assigns it automatically ✓
B. The user types it in by hand every time
A dynamic IP address is assigned automatically by the network (usually the router), so the user does not have to set it.
2. A laptop disconnects from school Wi-Fi and joins again the next day. What may happen to its dynamic IP address?
A. It is always exactly the same
B. It may be different from the day before ✓
Dynamic IP addresses can change each time a device connects. Only a static IP address stays fixed.
3. Which statement about a dynamic IP address is true?
A. It is permanently fixed to the device
B. It can change each time the device connects ✓
Being able to change is the key feature of a dynamic IP address. A fixed address is called a static IP address.
4. Phone A leaves the network. What can happen to the dynamic IP address it was using?
A. It can be reused by another device ✓
B. It can never be used again by anyone
Dynamic addresses are reused. When a device leaves, its address goes back to the pool and can be given to another device.
5. Which describes how a dynamic IP address is set up?
A. Assigned automatically when the device connects ✓
B. Set manually by a technician for each device
Automatic assignment is the point of a dynamic IP address. Manual setup is how a static IP address is usually configured.

Match the Pairs

IP address: 192.168.1.23 (assigned by router when laptop joins Wi-Fi) → A dynamic IP address: the network gives it to the device automatically when it connects
Monday: 192.168.1.23 | Tuesday: 192.168.1.41 → The same device has a different IP address each connection, so the address is dynamic
A dynamic IP address can be reused by another device after the first device disconnects → Phone leaves: 192.168.1.50 is free. Tablet joins: 192.168.1.50
A dynamic IP address is assigned automatically, not set by the user → Device joins network -> router gives it the next free address
A dynamic IP address never changes, so it is the same every time you connect. → Wrong: a dynamic IP address may change each time the device connects. An address that never changes is a static IP address.
The user must type in a dynamic IP address on each device before it can join the network. → Wrong: a dynamic IP address is given automatically by the network. Typing in a fixed address by hand is how a static IP is set.

Key Term

dynamic IP address
An IP address given to a device automatically by the network each time it connects, so it may change and can later be reused by another device.

Fill in the Blanks

1. ip ← network.assign(device)
Hint: Type the method name for the network automatically giving the device an address.
2. IF device.connects = TRUE THEN ip ← network.assign(device) ENDIF
Hint: Type the keyword that follows the condition in a pseudocode IF statement.
3. device.disconnect() network.release(oldIP)
Hint: Type the method name that frees an address so another device can reuse it.
4. ip1 ← network.assign(laptop) ip2 ← network.assign(laptop) OUTPUT ip1 ≠ ip2
Hint: Type the comparison operator showing the two addresses may differ between connections.
5. newIP ← network.assign(phone) phone.ip ← newIP
Hint: Type the variable that holds the address the network just gave to the phone.

Spot the Error

Question 1
A ipType <- "dynamic"
B device CONNECT network
C address <- network.ASSIGN()
D OUTPUT "Address is manual"
Line D — A dynamic IP address is assigned automatically by the network, not set manually. The line should say the address is automatic.
Question 2
A ip1 <- network.ASSIGN()
B device DISCONNECT
C device CONNECT
D ip2 <- ip1
E OUTPUT ip2
Line D — With a dynamic IP address the network assigns a new address each time the device connects, so it may differ. ip2 should be ip2 <- network.ASSIGN(), not a copy of ip1.
Question 3
A device CONNECT network
B ip <- USER.TYPE()
C device DISCONNECT
D network.RELEASE(ip)
Line B — The network gives out a dynamic IP address automatically. The user does not type it in. The line should be ip <- network.ASSIGN().
Question 4
A device1 DISCONNECT
B network.RELEASE(ip1)
C device2 CANNOT USE ip1
D OUTPUT "Address reused"
Line C — Once device1 disconnects, its dynamic address is released and can be reused by another device. It should say device2 CAN USE ip1.
Question 5
A ipType <- "static"
B device CONNECT network
C ip <- network.ASSIGN()
Line A — The network assigns the address automatically, so the type is dynamic. A static address is fixed and does not change. It should be ipType <- "dynamic".

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