Palo Alto Firewall Intrazone vs Interzone Traffic

 

Most organizations think “East-West traffic is trusted” and “Only North-South needs inspection.”
That assumption is exactly how lateral movement attacks succeed.

In Palo Alto Networks firewalls, Intrazone and Interzone traffic control is a core Zero Trust enforcement mechanism.

✅ 1) What is Interzone Traffic?
Interzone traffic = Traffic between different security zones.

📌 Example:
User Zone → Internet Zone
DMZ Zone → Trust Zone
Cloud Zone → Data Center Zone
👉 By default, Palo Alto blocks interzone traffic unless a security policy allows it.
Why it matters:
Interzone policies define business communication paths and attack surface boundaries.

✅ 2) What is Intrazone Traffic?
Intrazone traffic = Traffic within the same security zone.

📌 Example:
HR Server → Finance Server (both in Trust Zone)
User Laptop → File Server (same zone)
👉 By default, Palo Alto allows intrazone traffic unless explicitly blocked.
This is the most misunderstood part.
Most ransomware spreads inside the same zone, not across zones.

⚠️ Real Enterprise Risk Scenario
Imagine this architecture:
Trust Zone: Users, Servers, AD, File Servers
Internet Zone: External traffic
If one laptop gets compromised:
➡️ Intrazone default allow = attacker can move laterally
➡️ AD → File Server → Backup Server → Entire company encrypted
No firewall rule was broken. No alert was triggered.
This is why intrazone control is critical.

🛡️ How Top Security Teams Handle This
1️⃣ Enable explicit intrazone policies (deny by default model)
2️⃣ Micro-segment critical servers into separate zones
3️⃣ Use App-ID + User-ID for least privilege access
4️⃣ Log and inspect East-West traffic
5️⃣ Use Zone Protection + Threat Prevention profiles