DNS Checker.eu

Port Checker

Check whether a TCP port is open and reachable on any public host or IP, tested live from our EU servers, with one-click presets for the most common services.

About Port Checker

This port checker opens a real TCP connection from our servers to the host and port you specify and reports whether the connection succeeds. An open result means the full TCP handshake completed, so a service is listening and reachable from the public internet. Because the test originates outside your network, it reflects what the wider internet can actually reach - not merely what responds on localhost.

When a connection does not complete, the result is shown as closed or filtered, because the two cases are indistinguishable from outside over TCP. A closed port actively refuses the connection (nothing is listening), while a filtered port is silently dropped by a firewall or security group; both simply fail to connect. When a port is open, the checker also reports the connection latency in milliseconds and the resolved IP address it reached.

Preset chips fill in the well-known ports so you don't have to remember numbers: 21 (FTP), 22 (SSH), 25 (SMTP), 53 (DNS), 80 (HTTP), 110 (POP3), 143 (IMAP), 443 (HTTPS), 465 (SMTPS), 587 (Submission), 993 (IMAPS), 3306 (MySQL), 3389 (RDP), 5432 (PostgreSQL) and 8080. This makes it quick to confirm mail, web, database or remote-access services are exposed as intended.

The check runs server-side on EU infrastructure and probes a single TCP port over IPv4. For safety it refuses private and reserved addresses (such as 192.168.x.x or 10.x.x.x), so it only tests publicly routable hosts. Testing from a neutral external vantage point is exactly what you need to verify firewall rules, NAT mappings and cloud security-group changes.

How to use it

  1. 1Enter a public hostname or IP address to test.
  2. 2Type the port number, or click a preset chip such as 22 SSH, 443 HTTPS or 3306 MySQL.
  3. 3Run the check - our EU server attempts a TCP connection to that host and port.
  4. 4Read whether the port is open (a service is reachable) or closed/filtered, along with the connection latency when it is open.

Common use cases

  • -Confirm a newly added firewall rule or cloud security-group change actually exposes a service.
  • -Verify a mail server answers on 25, 465 or 587, or a database on 3306 or 5432, from outside your network.
  • -Troubleshoot connection-refused or timeout errors by testing reachability from a neutral vantage point.
  • -Check that a web server is listening on 80 and 443 after a deployment.
  • -Audit which well-known ports respond on a host you administer.

Frequently asked questions

What does it mean when a port is open?
Open means a full TCP handshake to that host and port succeeded, so a service is listening and reachable from the public internet. Because this tool connects from an EU server, the result reflects external reachability rather than what is available on localhost.
What is the difference between a closed and a filtered port?
Both fail to connect and look identical from outside. A closed port actively refuses the connection because nothing is listening, while a filtered port is silently dropped by a firewall. This checker reports either case as closed or filtered, since the two cannot be distinguished over TCP externally.
Does this tool scan UDP ports?
No. It performs a TCP connect test on a single port. UDP is connectionless and cannot be probed reliably with a simple connection attempt, so only TCP services are checked.
Can I check a port on my local or private network?
No. The test runs from our servers on the public internet, and private or reserved addresses such as 192.168.x.x or 10.x.x.x are rejected for security. Only publicly routable hosts can be reached.
Why is a port open on my machine but closed in this checker?
A firewall, NAT rule, or cloud security group is most likely blocking the port from outside even though the service listens locally. Testing from an external server reveals what the public internet can actually reach.
Which ports are most commonly checked?
Frequently tested ports include 22 (SSH), 25/465/587 (SMTP), 53 (DNS), 80 and 443 (HTTP/HTTPS), 3306 (MySQL), 5432 (PostgreSQL) and 3389 (RDP). Preset buttons fill these in with a single click.