Ports & Connectivity
Firewall Test: Verify Your Firewall Is Blocking Correctly
A misconfigured firewall can leave sensitive ports exposed to the internet without your knowledge. Our firewall test checks your public IP from an external perspective, verifying that ports are blocked as intended and flagging any unexpectedly open ports that could indicate a security issue.
Launch in Mission ControlWhat It Measures
This tool probes your public IP address for commonly exploited ports and reports whether each is open, closed, or properly filtered. It focuses on high-risk services like remote desktop, database servers, telnet, and management interfaces that should never be accessible from the internet.
How It Works
- Scans your public IP for high-risk ports from an external perspective
- Tests common attack targets: RDP (3389), Telnet (23), SMB (445), database ports
- Reports each port as properly blocked, accidentally open, or closed
- Generates a security rating based on the number of unnecessarily exposed ports
Why It Matters
Most home routers have basic firewall protection enabled by default, but misconfigured port forwarding rules, UPnP exploits, and ISP equipment issues can open ports unintentionally. A firewall test reveals what attackers see when they probe your IP address and identifies ports that need to be closed.
Understanding Your Results
A secure firewall should show all non-service ports as filtered (not just closed, as filtered ports reveal less information to attackers). Only intentionally public services should show open ports. Ports for RDP, Telnet, SMB, and database servers should never be accessible from the public internet.
Ready to test?
Run Firewall Test Now →Frequently Asked Questions
What is UPnP and why is it a firewall risk?
Universal Plug and Play (UPnP) allows devices and applications to automatically open ports on your router without manual approval. While convenient, UPnP has been widely exploited by malware and attackers to open unauthorized ports. Disabling UPnP on your router and manually managing port forwarding rules is more secure.
Should I be worried if a port shows as closed vs filtered?
Filtered is more secure than closed. A closed port responds with a reset packet, confirming the host exists at that IP. A filtered port drops packets silently, giving attackers less information about your network. Configuring your firewall to filter (drop) rather than reject packets is a best practice.
What are the most dangerous ports to leave open?
The most dangerous ports to leave publicly accessible include 3389 (RDP, frequently brute-forced), 445 (SMB, used by ransomware), 23 (Telnet, unencrypted), 3306 and 5432 (databases), 6379 (Redis, often exposed without authentication), and 27017 (MongoDB). Any of these open to the internet represents a serious security risk.
How do I block a port I cannot close?
Configure your router or firewall to drop packets destined for that port. On home routers, remove any port forwarding rules pointing to that port. In your OS firewall (Windows Defender Firewall or iptables on Linux), add inbound deny rules for the port. Check UPnP logs for automatically opened ports you did not authorize.
Related Tools
59+ Network Tools in One Dashboard
Mission Control gives you a complete terminal-style network diagnostics suite. Free, instant, no installation required.
Open Mission Control →