What is an open port?

An open port accepts inbound TCP connections on a host. A service (web server, SSH daemon, database) listens on that port number so clients can connect.

Is an open port dangerous?

Open ports are normal for public websites (80/443). Risk rises when admin ports (22, 3389, 3306) are exposed without patches, strong passwords, or IP allowlists.

What ports should be open for a website?

Typically TCP 80 for HTTP redirects and TCP 443 for HTTPS. Mail servers need 25/587/993 etc. on dedicated mail hosts — not usually on the same box as a small website.

What is the difference between TCP and UDP?

TCP is connection-oriented (web, SSH, email submission). UDP is datagram-based (DNS, VoIP, some games). This port checker focuses on TCP connectivity tests.

Why does a port show as filtered?

A firewall dropped probes without replying, or an ISP blocked the port. Filtered is inconclusive — the port might be open behind the filter for allowed IPs only.

How do I close an open port?

Stop the listening service or block the port in OS firewall, cloud security group, or router. Re-run the open port checker to confirm.

What is port forwarding?

Port forwarding on a home router sends inbound internet traffic on a public port to an internal LAN IP. Misconfiguration is a common reason port checks fail from outside.

Network Tools

Port Checker Online

Check whether a TCP port is open, closed, or filtered on any IP address or domain name.

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