GCSE · Computer Science · Edexcel · Spec 1CP2

Firewalls

Picture a bouncer who checks who's coming in AND what's being carried out. That's a firewall, and in a minute you get to be one.

Computer Science · Network security

Be the firewall

This network's rules: (1) block requests to suspicious websites; (2) block unauthorised apps from sending data out of the network; (3) block unauthorised attempts to get in from the internet; (4) let through anything the first three rules don't stop. Pick a flow of traffic, then choose where it goes.

Still to sort

Allow (0)

None of the blocking rules stops it.

Where the line is: Allowed doesn't mean ignored. The firewall still checked the traffic against its rules, and the rules let it through.

Block (0)

It breaks one of the security rules.

Where the line is: A flow is blocked because it breaks a rule. It makes no difference whether it is coming in or going out.

5 of 5 still to sort.

Rules on the board, traffic in the tray. You decide what gets through.

Why bother?

Reason it through

Why does a network need security at all?

Link 1 of 3

First link · your turn

What is travelling around a network all day?

Locked — reveal the link above first

Computer Science · Structure

Where the firewall sits

Tap the firewall to see what it does with traffic.

Tap any part of the diagram to see what it does.

Which idea is closest to yours?

What do you really think a firewall does?

Four people are explaining firewalls. Each sounds quite sure.

Which one is closest to what you think right now?

A firewall is there to stop attacks coming in from outside. What leaves the network isn't its business.Once a network has a firewall, it's completely safe.A firewall and a continuous network monitoring tool are the same thing under two names.A firewall filters traffic going in and out against security rules, and helps reduce the risk of attacks.

How sure are you?

I'm sureI think soI'm guessing

A firewall is there to stop attacks coming in from outside. What leaves the network isn't its business.

This is a common misconception

It sounds sensible, and it's the idea most people start with. But a firewall sits between the network and the internet and filters incoming AND outgoing traffic against its security rules. That is how it can stop an unauthorised app sending data out of the network.

Once a network has a firewall, it's completely safe.

This is a common misconception

Firewalls help reduce the risk of attacks and keep the network secure. That's reduce, not remove. A firewall can also be used alongside other tools, such as continuous network monitoring tools.

A firewall and a continuous network monitoring tool are the same thing under two names.

This is a common misconception

They do different jobs. The firewall filters traffic based on security rules. Continuous network monitoring tools detect unusual activity. They can be used together, which is exactly why they're not the same thing.

A firewall filters traffic going in and out against security rules, and helps reduce the risk of attacks.

This matches the evidence

That's the whole idea in one sentence. If you chose it, check you can say what an outgoing example looks like: an unauthorised app trying to send data out of the network.

In and out, against rules, reducing risk. A firewall is a gatekeeper with a rulebook, not a force field.

Your turn to write

Explain it in your own words

Describe how a firewall helps protect a network. [4 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

It acts as a barrier between the network and the internet. (1 mark)
It filters incoming and outgoing traffic. (1 mark)
It does this based on security rules. (1 mark)
It blocks unauthorised access or unauthorised flows of data, with an example such as blocking a suspicious website or stopping an unauthorised app sending data out. (1 mark)

Model answer

A firewall acts as a barrier between the network and the internet. It filters incoming and outgoing traffic based on security rules, so unauthorised access and unauthorised flows of data are blocked. For example, it might block access to a suspicious website or stop an unauthorised app from sending data out of the network.

Say both directions, say rules, and give one example. Those are the three things that are easy to leave out.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

the network's gatekeeper

What you need to know

Networks carry sensitive data, such as personal details and payment information, which could be stolen, lost or misused if unprotected.
Network security protects data, devices and users from threats such as malware and unauthorised access.
A firewall is a system that filters network traffic to protect against unauthorised flows of data in or out.
It acts as a barrier between a network and the internet.
It filters incoming and outgoing traffic, based on security rules.
Have a goYour mate Sam says: 'A firewall only checks what's coming IN. What leaves is the network's own business.' Sam sounds very sure. What has Sam missed?
A firewall filters outgoing traffic too, not just incoming.
It sits between the network and the internet and checks traffic in both directions against its security rules.
For example, a firewall might block access to a suspicious website.
Or it might stop unauthorised apps from sending data out of the network.
Have a goFinish this security rule so it would stop an app sending data out: 'Block any ______ app from sending ______ out of the network.'
unauthorised; data
A rule names a kind of traffic and what to do with it. This one targets unauthorised apps sending data out.
Firewalls block unauthorised access attempts.
They can be used alongside continuous network monitoring tools, which detect unusual activity.
Have a goTwo jobs: (a) filtering traffic against security rules, (b) detecting unusual activity. Which belongs to the firewall and which to a continuous monitoring tool?
(a) the firewall; (b) the monitoring tool.
They do different jobs, which is why they can be used alongside each other rather than one replacing the other.
Firewalls help reduce the risk of attacks and keep the network secure, but reduce is not the same as remove.

The big picture

A firewall is a system that filters network traffic, coming in and going out, against security rules. It acts as a barrier between a network and the internet and blocks unauthorised flows of data. It helps reduce the risk of attacks. It doesn't remove that risk.

Key points

1A firewall filters traffic in both directions, incoming and outgoing, between a network and the internet.

2It makes each decision by checking the traffic against security rules.

3It blocks unauthorised access attempts and unauthorised flows of data out of the network.

4A firewall helps reduce the risk of attacks. It does not remove the risk.

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Worked example

Problem

Using the same four rules as the sort, decide what the firewall does when the school's approved email app sends a teacher's message out to a parent.

⚠ Watch out

Thinking a firewall only watches for attacks coming in. It filters outgoing traffic too, which is how it can stop an unauthorised app sending data out of the network.

🧠

Memory hook

A firewall is a two-way gatekeeper with a rulebook: it checks what comes in AND what goes out.

✓

Check yourself

From memory: a firewall sits between a network and the internet. Which two kinds of traffic does it filter, what does it filter them against, and what is one example of traffic it might block?

Flashcards

(11)

Why do networks need security?

To protect data, devices and users from threats such as malware and unauthorised access.

Give two examples of sensitive data a network carries.

Personal details and payment information.

What could happen to sensitive data that isn't protected?

It could be stolen, lost or misused.

What is a firewall?

A system that filters network traffic to protect against unauthorised flows of data in or out of the network.

Where does a firewall sit?

As a barrier between a network and the internet.

Which traffic does a firewall filter?

Both incoming and outgoing traffic.

What does a firewall filter traffic against?

Security rules.

Example of outgoing data a firewall might stop?

An unauthorised app sending data out of the network.

Example of access a firewall might block?

Access to a suspicious website.

What can be used alongside a firewall to detect unusual activity?

Continuous network monitoring tools.

Does a firewall make a network completely safe?

No. Firewalls help reduce the risk of attacks and keep the network secure.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Be the firewall

Where the firewall sits

What do you really think a firewall does?

Explain it in your own words

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