Ports
Open Port Test: Verify External Port Reachability
If you are hosting a game server, running a self hosted service, or setting up port forwarding, you need to verify whether that port is actually reachable from the outside world. The Open Port Test connects to your specified port from our edge servers to confirm reachability.
What It Measures
This tool measures whether a TCP or UDP port on your IP address (or any IP you specify) is reachable from the public internet. It distinguishes between open (accepting connections), closed (actively refused), and filtered (no response, likely firewalled) states.
How It Works
- Initiates a TCP connect or UDP probe from a Pong.com edge server to your target port
- Tracks the connection state from open, closed, or filtered (timeout)
- Reports response time and any banner data exposed by the listening service
- Optionally tests common alternative ports if the primary fails
Why It Matters
Port forwarding setups frequently fail silently. Your router shows the rule, your service is running, yet outside users cannot connect. The Open Port Test verifies the entire chain from internet to your service. It is the standard way to confirm that game servers, Plex remote access, and self hosted apps are actually reachable.
Understanding Your Results
An open port responds within 100ms with a TCP SYN-ACK. A closed port responds with a RST. A filtered port times out, usually after 5 seconds, indicating a firewall is silently dropping packets. Connection latency should match your normal ping latency to the test server.
Frequently Asked Questions
Why is my port closed when my service is running?
Common causes include the service binding to localhost only (not 0.0.0.0), the local firewall blocking inbound connections, the router not having a port forwarding rule, the rule pointing to the wrong internal IP, or your ISP blocking that port. Work through each layer: local service, local firewall, router rule, ISP block.
What does 'filtered' mean?
Filtered means our probe got no response at all, neither acceptance nor refusal. This typically indicates a firewall is silently dropping the packets without responding. The firewall could be at any layer: your local OS firewall, your router, or your ISP. Filtered ports are common when your ISP blocks well known service ports like 25 (SMTP) or 80 (HTTP).
Do ISPs block specific ports?
Yes. Many residential ISPs block port 25 (SMTP outbound, to prevent spam), port 80 and 443 (HTTP and HTTPS inbound, to prevent home web hosting), and sometimes ports used for popular self hosted services. Business plans usually do not have these restrictions. Check your ISP's acceptable use policy if a specific port is unreachable.
How is this different from Port Checker?
Port Checker tests outbound connections from your network to common services. Open Port Test tests inbound connections from the public internet to your network. Use Port Checker to verify your network can reach external services. Use Open Port Test to verify external clients can reach a service you are hosting.
Related Tools
Browse all tools
Explore all 50+ network tools, from speed and latency to DNS, routing, and CDN diagnostics. Free, instant, no installation required.
See all network tools