A firewall rule is like a door rule — it decides who can come in or go out.
Every rule says:
➡️ Allow (let traffic pass)
or
⛔ Deny/Block (stop traffic)
💡 Simple Example:
Imagine your computer is your house, and the internet is the outside world.
| Situation | Rule Type | What It Does |
|---|---|---|
| You want to visit Google | ✅ Allow rule | Lets you access Google’s IP or website |
| You want to block Facebook | ⛔ Deny rule | Stops your computer from visiting Facebook |
| You only allow WhatsApp to use port 443 | ✅ Allow Port 443 | Lets WhatsApp connect securely |
| You block all other ports | ⛔ Deny All Other Ports | Keeps unknown apps from connecting |
⚙️ How Rules Work (in order)
Firewalls check rules from top to bottom:
- If a rule matches, it applies.
- If no rule matches, the firewall blocks by default (for safety).
🧠 Real-Life Example (Easy Words)
Let’s say you set these rules:
- Allow Google.com
- Block Facebook.com
- Allow WhatsApp port 443
Then:
- ✅ You can browse Google
- ⛔ Facebook won’t open
- ✅ WhatsApp works fine
🧰 Bonus Tip:
- In home routers, you can often find these settings under:
🔧 Firewall → Rules or Security → Access Control. - In corporate firewalls (like MikroTik, Fortigate, etc.), you set these by IP, port, or protocol.