How do I check if a TCP port is open online?

Enter your server's IP address or domain followed by a colon and the port number (e.g. 1.1.1.1:80 or example.com:443) and run a TCP check. The tool attempts a TCP handshake from 65+ global nodes and reports whether each connection succeeded, was refused, or timed out.

What is the difference between a port being refused versus timing out?

A refused connection (TCP RST) means the port is actively closed — the server replied to reject the connection. A timeout means no reply was received at all, which typically indicates a firewall is silently dropping packets before they reach the server or application.

Which TCP ports can I test?

Any valid TCP port from 1 to 65535. Common examples include port 80 (HTTP), 443 (HTTPS), 22 (SSH), 25 (SMTP), 3306 (MySQL), 5432 (PostgreSQL), and 3389 (RDP). No login or special permissions required — the check only verifies whether the TCP handshake completes.

My port is open locally but fails from external nodes — why?

If a port works locally but fails from external nodes, something between the internet and your server is blocking it — commonly a cloud security group, iptables rule, upstream ISP filter, or geoblocking policy. Running the check from multiple regions helps identify whether the block is global or specific to certain countries or ASNs.

Report for de-fra-nextserv.check-host.eu:80

Name: Check-Host de-fra-nextserv.check-host.eu:80 TCP 端口连通性测试
Author: Check-Host

Info Ping HTTP TCP UDP MTR DNS

Check TCP de-fra-nextserv.check-host.eu:80

Checked Jul 21, 2026 16:58:40 UTC |

| Check again |

Location	Result	Time	IP Address
Albania, Tirana	ERROR	-	195.123.4.45
Australia, Sydney	ERROR	-	195.123.4.45
Bosnia and Herzegovina, Novi Travnik	ERROR	-	195.123.4.45
Bulgaria, Sofia	ERROR	-	195.123.4.45
Brazil, São Paulo	ERROR	-	195.123.4.45
Canada, Montreal	ERROR	-	195.123.4.45
Switzerland, Bern	ERROR	-	195.123.4.45
Switzerland, Zurich	ERROR	-	195.123.4.45
Chile, Santiago	ERROR	-	195.123.4.45
China, Hohhot	ERROR	-	195.123.4.45
Germany, Nuernberg	ERROR	-	195.123.4.45
Germany, Frankfurt am Main	ERROR	-	195.123.4.45
Germany, Limburg	ERROR	-	195.123.4.45
Germany, Frankfurt am Main	ERROR	-	195.123.4.45
Germany, Frankfurt am Main	ERROR	-	195.123.4.45
Germany, Frankfurt am Main	ERROR	-	195.123.4.45
Germany, Koblenz	ERROR	-	195.123.4.45
Denmark, Glostrup Municipality	ERROR	-	-
Spain, Bilbao	ERROR	-	195.123.4.45
Spain, Barcelona	ERROR	-	195.123.4.45
Finland, Helsinki	ERROR	-	195.123.4.45
Finland, Helsinki	ERROR	-	195.123.4.45
France, Gravelines	ERROR	-	195.123.4.45
France, Paris	ERROR	-	195.123.4.45
United Kingdom, London	ERROR	-	195.123.4.45
Georgia, Tbilisi	ERROR	-	de-fra-nextserv.check-host.eu
Hong Kong, Hong Kong	ERROR	-	195.123.4.45
Croatia, Zagreb	ERROR	-	195.123.4.45
Hungary, Budapest	ERROR	-	195.123.4.45
Israel, Petach Tikwa	ERROR	-	195.123.4.45
Israel, Netanja	ERROR	-	195.123.4.45
India, New Delhi	ERROR	-	195.123.4.45
Iceland, Reykjavik (Miðborg)	ERROR	-	195.123.4.45
Italy, Como	ERROR	-	195.123.4.45
South Korea, Seoul	ERROR	-	195.123.4.45
Lithuania, Pilaite	ERROR	-	195.123.4.45
Latvia, Riga	ERROR	-	195.123.4.45
Moldova, Chisinau	ERROR	-	195.123.4.45
Netherlands, Amsterdam	ERROR	-	195.123.4.45
Netherlands, Amsterdam	ERROR	-	195.123.4.45
Netherlands, Amsterdam	ERROR	-	195.123.4.45
Netherlands, Amsterdam	ERROR	-	195.123.4.45
Netherlands, Eygelshoven	ERROR	-	195.123.4.45
Norway, Oslo	ERROR	-	195.123.4.45
Poland, Warsaw	ERROR	-	195.123.4.45
Romania, Bacău	ERROR	-	195.123.4.45
Romania, Bucharest	ERROR	-	195.123.4.45
Serbia, Belgrade	ERROR	-	195.123.4.45
Russia, Moscow	ERROR	-	195.123.4.45
Singapore, Singapore	ERROR	-	195.123.4.45
Tor, Onion	ERROR	-	de-fra-nextserv.check-host.eu
Tor, Onion	ERROR	-	de-fra-nextserv.check-host.eu
Tor, Onion	ERROR	-	de-fra-nextserv.check-host.eu
Turkey, Istanbul	ERROR	-	195.123.4.45
Turkey, Istanbul	ERROR	-	195.123.4.45
Taiwan, Taipei	ERROR	-	195.123.4.45
Ukraine, Khmelnytskyi	ERROR	-	195.123.4.45
United States, Dallas	ERROR	-	195.123.4.45
United States, Dallas	ERROR	-	195.123.4.45
United States, Los Angeles	ERROR	-	195.123.4.45
United States, Houston	ERROR	-	195.123.4.45
United States, Miami	ERROR	-	195.123.4.45
South Africa, Johannesburg	ERROR	-	195.123.4.45
South Africa, Johannesburg	ERROR	-	195.123.4.45