TCP exposure diagnostics

TCP Port Checker

Check whether selected TCP services are reachable on an authorised public IP address or domain.

Public targets only Up to 12 ports Live server check
01

Check TCP reachability

Enter a destination and a comma-separated list of ports.

Common:

Check only systems you own or have explicit permission to test. Results originate from the Zerolink server.

Interpret results carefully

What each port status means

Open

The destination accepted the TCP connection. Confirm that the exposed service is intentional, updated and access-controlled.

Closed

The host responded but refused the connection, normally because no service is listening or a firewall rejected it.

Filtered

No response arrived before timeout. A firewall or network policy may be silently dropping the connection.

Reduce unnecessary exposure

Restrict administration and database services to trusted addresses or a VPN. Use the Ping and Reachability Tool when the entire destination appears unreachable.

Port checker questions

What does an open TCP port mean?

An open result means the destination accepted a TCP connection on that port. It does not confirm that the service is secure or correctly configured.

What is the difference between closed and filtered?

Closed usually means the host actively refused the connection. Filtered means no response arrived before timeout, commonly because a firewall silently dropped the request.

Why does the tool show a different result from my computer?

The connection originates from the Zerolink hosting server. Firewalls, routing and geographic policies can produce different results from another network.

Which ports should normally be publicly open?

Only ports required by the intended public service should be exposed. Common examples are 80 and 443 for websites; administrative and database ports should usually be restricted.

Does an open port prove that my system is vulnerable?

No. It confirms reachability only. Vulnerability assessment requires authorised service identification, configuration review and security testing.