A school with locked corridors
A school has a main gate, and inside, locked corridors. Pupils reach classrooms. Only staff reach the office. Nobody but the caretaker reaches the boiler room.
A good network (computers joined together) is built the same way. There is a guard at the gate, zones inside and someone watching the cameras.
Today you learn rules for the firewall (the gate guard), keeping networks apart and watching traffic.
By the end of this lesson
Note
I can describe how a firewall is configured, how networks are kept apart and how traffic is watched.
Key words
| Word | What it means |
|---|---|
| Firewall | A guard that decides which network traffic may pass. |
| Rule | One instruction in a firewall: allow or deny this traffic. |
| Inbound | Traffic coming into a network. |
| Outbound | Traffic leaving a network. |
| Port | A numbered door on a computer for one kind of traffic. |
| IP address | The number that names a computer on a network. |
| Segregation | Keeping parts of a network apart. |
| VLAN | Virtual LAN: one physical network split by software into separate groups. |
| Monitoring | Watching traffic and logs all the time to spot problems. |
| Network | Computers joined together so they can share data. |
| Protocol | A set of rules for how computers talk. |
The cells students fill in are left blank in this preview.
Starter: what you already know
Have a go
Starter: what you already know
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Cycle 1: firewall rules
A firewall checks traffic against a list of rules. Each rule says allow or deny.
Direction: an inbound rule is for traffic coming in. An outbound rule is for traffic going out. You may block both.
Good practice: deny everything, then allow only what is needed. The first rule that matches decides.
Four ways to write a rule
Traffic type rules: by kind of traffic, such as web, email or file transfer (a protocol).
Application rules: by the program, for example allow a video call app but block a file sharing app.
IP address rules: by where traffic comes from or goes to. Block a bad address. Allow only the office.
Port rules: by port number, such as allow 443 and deny 23.
Worked example: a small firewall list
| Order | Direction | Port | Action | Why |
|---|---|---|---|---|
| 1 | In | 443 | Allow | The secure web site must be reachable |
| 2 | In | 22 | Allow, only from the office address | Staff remote login, limited by IP address |
| 3 | In | 23 | Deny | Old unsafe remote login |
| 4 | Out | 25 | Deny, except the mail server | Stops infected computers sending spam |
| 5 | Any | Any | Deny | Everything else is blocked |
The cells students fill in are left blank in this preview.
Check: firewall rules
Have a go
Check: firewall rules
4 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.