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Open Port Checker

Test whether a port on your connection is reachable from the public internet

Is my port open?

A port only counts as open if a connection can reach it from outside your network. Checking on your own machine cannot prove that, because local tools never leave your LAN. This checker probes your public IP from our server, so you get the same view the internet has - the real test for port forwarding, game servers, and remote access.

Scanning your IPDetecting...

We only ever scan your own public IP, read from your connection - never a third party. Nothing you enter targets anyone else.

Choose ports to check

Ready to check: 80, 443, 25565

Open vs closed vs filtered: what each result means

  • Open: a service answered from the public internet on that port. Port forwarding and firewall rules are working.
  • Closed: your host is reachable but nothing is listening on that port. The forward may be missing, the app is not running, or the wrong internal device is targeted.
  • Filtered: no response at all. A firewall, your router, or carrier-grade NAT is dropping the connection before it reaches you. This is the classic CGNAT symptom.

If ports stay filtered no matter what you forward, the problem is usually upstream of your router. Confirm it with the CGNAT test and compare your router WAN IP with your public IP.

Verify each layer

How this open port checker works

When you pick a port, we open a TCP connection to your public IP on that port from our server and watch what happens:

  1. The connection completes, so a service is listening and the port reads as open.
  2. The connection is actively refused, so the host is reachable but nothing is listening - the port is closed.
  3. Nothing answers before the timeout, so a firewall or NAT is silently dropping it - the port is filtered.

For privacy and safety, this tool only ever scans your own public IP, read from your connection at the edge. It cannot be pointed at anyone else, so it is a diagnostic for your own port forwarding, not a scanner for third-party hosts.

What to do after the check

Match the next step to what the result told you.

1Next step
Diagnose

Rule out CGNAT

If ports are filtered, confirm whether carrier-grade NAT is blocking inbound connections before it reaches your router.

Run CGNAT test
2Next step
Resolve

Fix port forwarding

Walk through UPnP, manual forwards, IPv6, and reverse tunnels when the port will not open.

Read the fixes
3Next step
Context

Confirm your network

Use your public IP to verify which ISP or carrier is announcing your route before contacting support.

Open ASN lookup

Related Articles

CGNAT Port Forwarding Not Working? Fix It in 20269 min read • June 3, 2026CGNAT IP Range: 100.64.0.0/10 Explained (RFC 6598)13 min read • January 17, 2026What Is a Router? Definition, Functions, and Types11 min read • April 5, 2026Public vs Private IP Addresses Explained13 min read • December 2, 2025Router Login Guide: 192.168.1.1, 192.168.0.1, 10.0.0.1 and Default Gateway Basics9 min read • February 23, 2026

Frequently asked questions

How do I check if a port is open?
A port is only truly open if it is reachable from the public internet, so the test has to come from outside your network. This tool opens a connection to your public IP on the port you choose and reports open, closed, or filtered. Checking locally on your own computer cannot confirm outside reachability.
Why is my port showing as filtered?
Filtered means nothing responded before the timeout, which usually means a firewall, your router, or carrier-grade NAT (CGNAT) is dropping the connection. If forwarding never works, run the CGNAT test: if your router WAN IP is inside 100.64.0.0/10, no port forward on your router will reach you.
What is the difference between closed and filtered?
Closed means your host answered and actively refused the connection, so it is reachable but nothing is listening on that port. Filtered means there was no answer at all, so something between us and you is silently blocking it. Closed points at your service or forward; filtered points at a firewall or NAT.
Can I use this to scan someone else’s IP or a website?
No. For privacy and safety this tool only scans your own public IP, detected from your connection. It never accepts a target address, so it cannot be used to port-scan other people, servers, or internal networks.
Does an open port mean my network is unsafe?
Not by itself. An open port is only a risk if the service behind it is outdated, misconfigured, or exposed unintentionally. If you deliberately forwarded a port for a game server or remote access, open is the expected result. Close ports you are not using and keep exposed services patched.
Why does the checker say my IP is not reachable?
If your public IP is a private (RFC1918) or CGNAT (100.64.0.0/10) address, it is not routable from the internet, so no port can be open. That is a sign your ISP places you behind carrier-grade NAT and you need a public IPv4, IPv6, or a reverse tunnel to accept inbound connections.