← ACARA Digital Technologies Years 9–10

DHCP

Dynamic Host Configuration Protocol: a router service that automatically gives each joining device an IP address, subnet mask and default gateway, so no manual set-up is needed.

Part of: ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 22, WA Computer Science ATAR Year 11 — Network Communications — Module 45

Understanding DHCP in ACARA Digital Technologies Years 9–10

What it does: Choosing automatic or DHCP in a device's network settings means the student does not type in an address by hand. The DHCP server picks unused addresses from its pool and never gives the same one to two devices, so conflicts are avoided. With DHCP there is no manual set-up, so the device is ready to use quickly. A lease runs out after a set time. The device can renew it, or the address goes back to be used again. The broken code describes manual set-up, which is the opposite of what DHCP does. Avoiding address conflicts is a key job of DHCP, so handing out a duplicate address is wrong.

Common mistakes: With DHCP the device asks the router for an address, so no manual set-up is needed. Line 2 should be: device sends DHCP discover. 192.168.1.300 is not a valid IPv4 address because each part can only go up to 255. The default gateway should be the router's real address, 192.168.1.1.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 12–34) and word search (Modules 12–55).

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Learning

Duo

What does DHCP do when a phone joins the home Wi-Fi?

It makes the phone type in its own IP address by handIt automatically gives the phone an IP address, subnet mask and default gateway

Matches

DHCP: every new phone must be given an IP address by typing it in by hand

↓

DHCP works automatically, so no one needs to type in an address by hand. Manual typing is a static IP address.

Applying

Meanings

Term

DHCP

Meaning

Dynamic Host Configuration Protocol: a router service that automatically gives each joining device an IP address, subnet mask and default gateway, so no manual set-up is needed.

Practice

DHCP service ON

Testing

Gaps

gives joining devices an IP address

Check Answer

Spots

1device joins the network

2device sets its IP by hand

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Quick Questions

1. What does DHCP do when a phone joins the home Wi-Fi?

A. It automatically gives the phone an IP address, subnet mask and default gateway ✓

B. It makes the phone type in its own IP address by hand

DHCP hands out the network settings automatically, so nobody has to set them up manually.

2. Where is the DHCP service usually running on a home network?

A. On the router ✓

B. On the phone or laptop that joins

Home routers include a DHCP service that gives settings to each device that joins.

3. Which settings does DHCP hand to a joining device?

A. MAC address, password and web page

B. IP address, subnet mask and default gateway ✓

DHCP gives out the IP address, subnet mask and default gateway. A MAC address is built into the device's network adapter.

4. Mia plugs a new laptop into the network and can browse straight away without typing any settings. Why?

A. DHCP set up the network settings for her automatically ✓

B. The laptop already knew every IP address on the network

With DHCP there is no manual set-up, so the device is ready to use quickly.

5. What is an address lease in DHCP?

A. An IP address that a device owns forever

B. An IP address given to a device for a set amount of time ✓

A lease runs out after a set time. The device can renew it, or the address goes back to be used again.

Match the Pairs

DHCP → A router service that automatically gives each joining device an IP address, subnet mask and default gateway

lease_time = 24h → How long a device may keep its assigned IP address before it must renew it or give it back

DHCP removes manual set-up: a new device joins and gets its network settings automatically → ip_settings = auto (DHCP)

DHCP avoids address conflicts by giving each device a different address from its pool → pool = 192.168.1.100 - 192.168.1.200

DHCP: every new phone must be given an IP address by typing it in by hand → DHCP works automatically, so no one needs to type in an address by hand. Manual typing is a static IP address.

DHCP gives two laptops the same IP address 192.168.1.50 at the same time → DHCP keeps track of its leases, so it never gives one address to two devices at once. Two devices with the same address would cause a conflict.

Key Term

DHCP

Dynamic Host Configuration Protocol: a router service that automatically gives each joining device an IP address, subnet mask and default gateway, so no manual set-up is needed.

Fill in the Blanks

1. DHCP gives joining devices an IP address

Hint: Type the four-letter name of the service that hands out addresses automatically.

2. DHCP gives IP, mask and default gateway

Hint: Type the word for the router address a device uses to reach other networks.

3. DHCP address lease = time an IP is borrowed

Hint: Type the word for the length of time a device may keep its address before renewing.

4. DHCP sets up devices automatically

Hint: Type the adverb meaning no manual set-up is needed.

5. DHCP gives each device a unique address

Hint: Type the word meaning no two devices share the same address, which avoids conflicts.

Spot the Error

Question 1

A device joins the network

B device sets its IP by hand

C router offers an IP address

D device accepts the offer

Line B — With DHCP the device asks the router for an address, so no manual set-up is needed. Line 2 should be: device sends DHCP discover.

Question 2

A DHCP server settings

B range = 192.168.1.50-100

C mask = 255.255.255.0

D gateway = 192.168.1.300

Line D — 192.168.1.300 is not a valid IPv4 address because each part can only go up to 255. The default gateway should be the router's real address, 192.168.1.1.

Question 3

A DHCP gives out MAC addresses

B it also gives a subnet mask

C and a default gateway

Line A — MAC addresses are built into the hardware and are not handed out. DHCP gives out IP addresses.

Question 4

A lease = 8 hours

B time_left = lease + used

C if time_left == 0:

D address returns to pool

Line B — Time left on a lease is the lease length minus the time already used. Adding would make the time left grow, so line 2 should use a minus sign.

Question 5

A pool = [10, 11, 12]

B give 10 to phone

C give 10 to laptop

D mark 10 and 11 as used

Line C — The phone already has address 10, so giving 10 to the laptop would cause an address conflict. DHCP gives the laptop a different free address, such as 11.

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