Open Port Checker
Check from the internet whether ports are open, closed or filtered on a server or router – port forwarding, firewalls, mail, RDP, SSH and VPN in one test.
Is the port forward on your router working? Is your mail server reachable on port 25? Did someone leave Remote Desktop open to the internet? This checker connects from our server to the ports you list and reports each one as open, closed or filtered – exactly what anyone on the internet sees.
How to use it
- Enter your public IP address (see What Is My IP) or a hostname such as
mail.example.com. - Pick a common set – website, mail, VPN – or type up to 10 ports, e.g.
22, 443, 8000-8005. - Press Check ports and read the state of each port.
Open, closed or filtered?
- Open – a service answered. That’s what you want for websites, mail and VPNs.
- Closed – the host is reachable but nothing listens on that port: the service is stopped or listens on another port.
- Filtered – no answer at all: a firewall drops the traffic, the port forward is missing, or the ISP blocks the port.
Port forward not working?
Check, in order: the service is running and listening on 0.0.0.0 (not only 127.0.0.1); the forward points to the device’s current LAN IP; the device’s own firewall allows the port; and your router’s WAN IP matches your public IP – if it doesn’t, your ISP uses CGNAT and inbound connections can’t reach you.
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What is the difference between closed and filtered?
Closed means the host answered and said nothing is listening. Filtered means there was no answer at all – a firewall silently dropped the connection. Both stop traffic; filtered hides that the host exists.
My port forward doesn’t work – what should I check?
Make sure the service is running and listening on the right interface, the forward points at the device’s current LAN IP, the device’s own firewall allows the port, and your ISP isn’t using CGNAT (your router’s WAN IP differs from your public IP).
Why can’t I check UDP ports?
UDP has no handshake, so a port that doesn’t reply looks the same whether it’s open or blocked. This checker tests TCP; for UDP services such as WireGuard, test the service itself.
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