Network foundations · Lesson 4 of 5
Read a firewall rule as a sentence
A firewall controls traffic according to rules. Reading a rule is easier when you turn it into a sentence: allow this source to reach that destination using this protocol and port.
Read the rule across the row
Fictional application and database addresses; not targets to connect to.
| Rule field | Example value | Meaning |
|---|---|---|
| Source | 192.0.2.10 | The app server |
| Destination | 192.0.2.20 | The database |
| Protocol / port | TCP / 5432 | The required database service |
| Action | Allow | Permit this specific flow |
Read the visualWhy not allow every source on every port?
That grants more network access than the stated task requires. Keep both endpoints and the service specific.
Identify both ends
The source starts the conversation; the destination receives it. Decide which systems actually need to communicate.
Name the service
A network port is a numbered communication endpoint, not a physical socket. A rule can distinguish traffic by protocol and port.
Keep the permission specific
A broad rule can permit unnecessary connections. Allow the required flow, document its purpose, and review it when the application changes.
Put it in context
A fictional app server at 192.0.2.10 needs to reach its database at 192.0.2.20 on TCP port 5432. A rule allowing that exact flow is narrower than allowing every source to every database port. These addresses are examples, not systems to connect to.
Read the source, destination, protocol, port, and action together.
Read the sources
Make it stick.
Try one short question to check your understanding and save this lesson to your progress.