Troubleshooting Mindset: 7 Questions I Always Ask Before Blaming the Firewall

Over the years, I've learned that jumping straight into firewall configuration changes usually creates more problems than it solves.

Instead, I follow a simple troubleshooting checklist before touching any security policy.

1️⃣ Can the client reach the destination?

Start with the basics.

Ping
Traceroute
Test-NetConnection
Pathping (if available)

If Layer 3 connectivity is already failing, the firewall may not even be involved.

2️⃣ Is DNS resolving correctly?

One incorrect DNS record can make an application appear "offline."

Always verify with:

nslookup application.company.local

or

dig application.company.local

If the IP address is wrong, changing firewall policies won't fix the issue.

3️⃣ Is the firewall actually blocking the traffic?

Never assume.

Always verify:

Security Logs
Traffic Logs
Session Logs
Hit Count on Policies

If there's no matching session, the problem may be elsewhere.

4️⃣ Did anything change recently?

Ask these questions:

Was there a firewall policy update?
Was the application migrated?
Was DNS modified?
Was the server patched?
Was there a routing change?

Many incidents are triggered by recent changes.

5️⃣ Can the server receive connections?

Try accessing the server directly.

Examples:

telnet <server-ip> 443

or

Test-NetConnection <server-ip> -Port 443

Sometimes the application service is down—not the network.

6️⃣ Is NAT working as expected?

Misconfigured NAT rules can cause:

Connection failures
Incorrect source IP addresses
Asymmetric routing
Unexpected application behavior

Always review NAT before creating new policies.

7️⃣ What do the logs actually tell you?

Logs tell a story.

Instead of asking:

"Why isn't this working?"

Ask:

"What evidence do I have?"

Every investigation should be guided by logs—not assumptions.

Solid checklist — the "evidence over assumptions" mindset in step 7 is really the core discipline.

but it's worth keeping a hard rule alongside your existing one — no policy change without a rollback plan and a documented before-state, even after all this diagnosis confirms the firewall is the culprit. That keeps the checklist's discipline intact all the way through the fix, not just the investigation.

Thanks for sharing!

Thanks to share!

Hi,
The best firewall engineers don't start by changing the configuration. They begin by gathering evidence, reviewing the logs, and understanding exactly what's happening before making any changes.
A few extra minutes spent analyzing the logs can save hours of unnecessary troubleshooting and prevent new problems from arising.