Firewall Port Tester

Test if your firewall configuration allows or blocks specific ports from different geographic locations.

What This Checks

Multi-region port checkCommon port presetsSingle port verificationTCP connectivity testFirewall testing

About Port Checker

Test if specific TCP ports are open and accessible from multiple global locations. Check common ports like HTTP (80), HTTPS (443), SSH (22), and more.

Key Features

Multi-region port check

Common port presets

Single port verification

TCP connectivity test

Firewall testing

Also Available via API & MCP Server

Automate port checker checks in your CI/CD pipelines or run them directly from your AI coding agent.

REST API

Single endpoint, JSON response. Integrate into any language or platform.

cURL

curl -X POST https://probeops.com/api/v1/run \
  -H "X-API-Key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"tool": "port_check", "target": "example.com"}'

Learn more about the API

MCP Server

Works with Claude Code, Cursor, Windsurf, and any MCP-compatible IDE.

Claude Code

> Check the port checker for example.com

Claude uses the probeops_port_check tool to run
the check from 6 global regions and returns
structured results.

Learn more about the MCP Server

Firewall port testing verifies whether firewall rules are correctly allowing or blocking traffic to specific ports. Misconfigured firewalls are a leading cause of "it works locally but not from outside" issues—testing from external locations confirms your firewall behaves as expected.

Our multi-region firewall tester checks port accessibility from 6+ global locations, revealing inconsistencies in firewall rules, security groups, or ISP-level blocking. This is invaluable for validating cloud security group configurations, troubleshooting VPN access, and auditing server exposure.

For complete security validation, also run SSL checker on HTTPS ports and use traceroute to verify the network path if ports appear blocked.

**Methodology:** TCP connect from 6 external regions testing firewall pass-through, with clear open/closed/filtered status per region.

Common Errors & How to Fix Them

3 relevant issues

What This Means

No response received—a firewall is silently dropping packets to this port. The port may or may not have a service listening.

How to Fix

1) Check local firewall: ufw status, iptables -L -n. 2) For cloud: check security groups (AWS), firewall rules (GCP), NSG (Azure). 3) Check host-level firewall (Windows Firewall). 4) Verify ISP isn't blocking: test from different network. 5) Add firewall rule: ufw allow PORT/tcp.

port filteredfirewallblockedno response

What This Means

The port actively refused the connection. Either no service is listening on this port, or it's configured to reject connections.

How to Fix

1) Verify service is running: systemctl status service-name. 2) Check service is on correct port: netstat -tlnp | grep PORT. 3) Ensure service binds to 0.0.0.0, not 127.0.0.1. 4) Check service configuration for listen address/port. 5) Restart service: systemctl restart service-name.

port closedconnection refusedservice not running

What This Means

The connection attempt timed out. Server may be overloaded, port may be filtered, or there's network congestion.

How to Fix

1) Try with longer timeout: nc -vz -w 10 host port. 2) Check if server is overloaded: verify other services respond. 3) Test from different location to rule out network issues. 4) Check server resources: CPU, memory, connection limits. 5) Review firewall logs for dropped packets.

timeoutconnection timeoutslow response

See all errors →

Frequently Asked Questions

4 relevant questions

Common causes: 1) Firewall blocking the port (check iptables/ufw/Windows Firewall), 2) Service bound to localhost only (127.0.0.1) instead of 0.0.0.0, 3) Security group rules (AWS/cloud), 4) ISP blocking the port, 5) Service crashed after starting. Check with: netstat -tlnp | grep PORT or ss -tlnp | grep PORT.

port-checkertroubleshooting

"Open" means a service is listening and accepting connections. "Closed" means no service is listening—the port actively rejects connections. "Filtered" means a firewall is blocking access—no response is received. From a security perspective, filtered is better than closed, as it doesn't confirm the port exists.

port-checkerstatus

A port might be accessible from one region but blocked from another due to: geo-restrictions, ISP-level blocking, cloud security groups configured per region, or CDN/proxy rules. Multi-region port checking reveals access inconsistencies and helps diagnose "works locally but not from X" issues.

port-checkerregions

Open ports themselves aren't insecure—the services behind them might be. Only expose necessary ports. Use firewalls to restrict access by IP when possible. Keep services updated to patch vulnerabilities. For admin services (SSH, databases), use non-default ports and require VPN/bastion access. Regularly audit which ports are open.

port-checkersecurity

See all FAQs →

How to Check if Ports are OpenStep-by-step guide with examples and troubleshooting tips