← ACARA Digital Technologies Years 9–10

MAC address filtering

A router setting that only lets devices with MAC addresses on an allowed list join. It is easy to set up but weak, because a MAC address can be copied (spoofed).

Part of: ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 127, WA Computer Science ATAR Year 11 — Network Communications — Module 110, WA Computer Science ATAR Year 11 — Cyber Security — Module 122

Understanding MAC address filtering in ACARA Digital Technologies Years 9–10

What it does: The router checks each device's MAC address against its allow list. It accepts a match and blocks anything else. Using both controls gives layered security. An attacker must copy an allowed MAC address and also know the Wi-Fi password. Spoofing means pretending to be an allowed device by copying its MAC address. MAC filtering is a simple router setting, which is why people use it. But easy does not mean strong. No single control is enough. Using MAC filtering as one layer with a strong password makes the network harder to break into. A DNS domain table matches names to IP addresses. MAC filtering uses a list of allowed MAC addresses.

Common mistakes: MAC filtering needs allow list mode so only listed devices can join. Allowing everyone turns the filter off. It should be: SET mode TO allow_list. A device whose MAC address is on the allowed list should be let in. Line 4 blocks it. It should be: allow_join().

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This module's key terms are also in a printable crossword (Modules 116–154) and word search (Modules 116–225).

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Learning
Duo
What does MAC address filtering on a router do?
It only lets devices whose MAC addresses are on an allowed list join the networkIt scrambles all data so nobody can read it
Matches
mac_filter = on # now the network is fully secure
↓
MAC filtering alone does not make a network fully secure, because MAC addresses can be copied (spoofed). It should be layered with a strong Wi-Fi password.
Applying
Meanings
Term
MAC filtering
Meaning
A router setting that only lets devices with MAC addresses on an allowed list join. It is easy to set up but weak, because a MAC address can be copied (spoofed).
Practice
allowList ← ["A4:5E:60:C1:22:9F", "3C:22:FB:08:7D:41"]
Testing
Gaps
IF deviceMac allowedList THEN
Check Answer
Spots
1SET mode TO allow_everyone
2ADD aa:bb:cc:11:22:33 TO list

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Quick Questions

1. What does MAC address filtering on a router do?
A. It scrambles all data so nobody can read it
B. It only lets devices whose MAC addresses are on an allowed list join the network ✓
MAC filtering is an allow list. The router checks each device's MAC address and blocks any that are not on the list.
2. Mia adds her phone's MAC address to her router's allow list. Her friend's laptop is not on the list. What happens when the laptop tries to join?
A. The router lets the laptop join because it knows the Wi-Fi password
B. The router refuses the laptop ✓
With MAC filtering on, a device not on the allow list is blocked, even if it has the right password.
3. Why is MAC filtering considered a weak form of security on its own?
A. A MAC address can be copied (spoofed) by an attacker ✓
B. A MAC address changes every time a device connects
MAC addresses are sent in the clear, so an attacker can see an allowed one and copy it onto their own device. This is called spoofing.
4. An attacker watches the Wi-Fi and sees an allowed MAC address. What can they do?
A. Set their own device to use that MAC address (spoof it) to get past the filter ✓
B. Nothing, because the filter hides every MAC address
Spoofing means pretending to be an allowed device by copying its MAC address.
5. Which is true about setting up MAC filtering?
A. It is easy to set up: you type each allowed MAC address into the router's list ✓
B. It is hard to set up: you must install special encryption software on every device
MAC filtering is a simple router setting, which is why people use it. But easy does not mean strong.

Match the Pairs

allow 3C:52:82:1A:9F:07 → Adds this device's MAC address to the router's allow list so it can join the network
spoof_mac(laptop, 3C:52:82:1A:9F:07) → Makes a device pretend to have another device's MAC address, which can trick MAC filtering
MAC filtering only accepts devices on the allow list and blocks all others → if mac in allow_list: accept() else: block()
Layer MAC filtering with a strong Wi-Fi password so one weak control is not the only protection → wifi_password = strong mac_filter = on
mac_filter = on # now the network is fully secure → MAC filtering alone does not make a network fully secure, because MAC addresses can be copied (spoofed). It should be layered with a strong Wi-Fi password.
allow_list = [guest_phone] # phone uses its IP address → MAC filtering uses MAC addresses, not IP addresses. The allow list should contain the phone's MAC address, such as 3C:52:82:1A:9F:07.

Key Term

MAC filtering
A router setting that only lets devices with MAC addresses on an allowed list join. It is easy to set up but weak, because a MAC address can be copied (spoofed).

Fill in the Blanks

1. IF deviceMac IN allowedList THEN ALLOW device ELSE DENY device
Hint: Type the keyword that checks whether the device's MAC address is a member of the allowed list.
2. allowedList = ["A4:5E:60:C1:22:9B"] router.macFilter = ON
Hint: Type the setting value that switches the MAC filter on for the router.
3. attackerMac = allowedMac IF attackerMac IN allowedList THEN ALLOW attacker
Hint: The copied (spoofed) address matches the list. Type the action the router wrongly takes.
4. IF macOk AND passwordOk THEN ALLOW device ELSE DENY device
Hint: Type the logical operator that requires both the MAC filter check and the Wi-Fi password check to pass.
5. IF deviceMac NOT IN allowedList THEN DENY device
Hint: Type the logical word that reverses the check so unlisted devices are caught.

Spot the Error

Question 1
A SET mode TO allow_everyone
B ADD aa:bb:cc:11:22:33 TO list
C SET filtering TO on
Line A — MAC filtering needs allow list mode so only listed devices can join. Allowing everyone turns the filter off. It should be: SET mode TO allow_list
Question 2
A device = new_phone
B mac = device.mac
C IF mac IN allowed_list THEN
D block_join()
E ELSE
F block_join()
Line D — A device whose MAC address is on the allowed list should be let in. Line 4 blocks it. It should be: allow_join()
Question 3
A allow = ['A1:B2:C3:D4:E5:F6']
B if mac not in allow:
C print('Joined')
D else:
E print('Blocked')
Line B — This test lets in devices that are NOT on the allow list and blocks the ones that are. It should be: if mac in allow:
Question 4
A attacker sniffs the Wi-Fi
B attacker sees an allowed MAC
C attacker keeps their own MAC
D router thinks it is trusted
Line C — Spoofing means copying an allowed MAC address. If the attacker kept their own MAC, the router would not trust them. It should be: attacker copies the MAC
Question 5
A SET wifi_password TO strong
B SET mac_filter TO on
C RESULT: use MAC filter alone
Line C — MAC filtering is weak because MACs can be spoofed, so it should be layered with a strong Wi-Fi password. It should be: RESULT: use both together

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