How Does the Port Checker Work?
A port check tells you whether a service running on your computer or on another device in your network can be reached from the internet. When you start a test, our server tries to open a TCP connection to your own public IP address on the port you chose and waits up to 3 seconds for an answer. In a few seconds you'll know whether your port forwarding rule, your security camera or DVR, or your game server is visible from the outside.
- To keep the tool from being abused to scan other people's networks, it only tests your own IP address; you can't enter a different one.
- Only TCP ports are tested. UDP is connectionless, so it can't be checked reliably this way.
- Each IP address can run up to 6 checks per minute.
What Do the Results Mean?
| Result | Meaning |
|---|---|
| Open | The connection was accepted: port forwarding works and a service is listening. |
| Closed | Your device or router answered but refused the connection. Your IP address is reachable, but nothing is listening on that port: the program isn't running, or the forwarding rule is missing or points to the wrong device. |
| Filtered | No answer arrived within 3 seconds. A firewall is silently dropping the packets, the router has no forwarding rule, you're behind CGNAT or your ISP blocks the port. |
| Unsupported | The test couldn't be run for this connection, for example because our server can't reach your IPv6 address. |
Why Is My Port Closed or Filtered?
- CGNAT: one of the most common reasons for a “filtered” result, especially on mobile connections. If the WAN (internet) IP address shown in your router's admin page is in the
100.64.0.0/10range (100.64.x.xto100.127.x.x), your public IP is shared with other customers and incoming connections never reach you. The fix is to ask your ISP for a public or static IP address. - Missing or wrong forwarding rule: the rule may not exist, may point to an old local IP address or may use the wrong protocol.
- Double NAT: if you have your own router behind the ISP's modem, you need to forward the port on both devices or put the modem in bridge mode.
- The device's firewall: software such as Windows Defender Firewall can block incoming connections.
- The service isn't running: the program, game server or camera must be on and listening on that port while you test.
- ISP blocking: some providers block certain ports, such as 25 or 445, for security reasons.
For step-by-step instructions, read our port forwarding guide; for CGNAT and public IP addresses, see the static IP guide.
If You're Connected over IPv6
If you reached this site over IPv6, the test targets your IPv6 address. IPv6 doesn't use NAT, so port forwarding rules play no part; instead, you need to allow incoming connections to that device and port in your router's IPv6 firewall. Since port forwarding is usually set up for IPv4, you can temporarily disable IPv6 on your device and reload this page to test your IPv4 rule.
Commonly Tested Ports
| Port | Service | Notes |
|---|---|---|
| 80 / 443 | HTTP / HTTPS | Web servers and device admin pages |
| 554 | RTSP | Live video streams from IP cameras |
| 8000 | Hikvision / HTTP | Client (SDK) port of Hikvision recorders |
| 34567 / 37777 | XMEye / Dahua DVR | Remote camera viewing from mobile apps |
| 25565 | Minecraft | Java Edition server (TCP) |
| 27015 | Steam / CS2 | Game traffic is mostly UDP, so a TCP test only tells part of the story. |
| 32400 | Plex | Remote access to Plex Media Server |
| 1194 | OpenVPN | Uses UDP by default; a TCP test only makes sense in TCP mode. |
| 3389 | RDP | Windows Remote Desktop; never expose it directly. |
Which Ports Should You Never Open?
Bots scan the entire internet for open ports around the clock. Don't expose RDP (3389), SMB (445) or Telnet (23) directly to the internet: they're among the most common targets of ransomware and password-guessing attacks. For remote access, use a VPN, such as the VPN server built into many routers, change the default passwords on cameras and DVRs, and delete forwarding rules you no longer need.