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 50+ 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 it-com-lake.check-host.eu:80

Name: Check-Host it-com-lake.check-host.eu:80 TCP 連接埠連通性測試
Author: Check-Host

Info Ping HTTP TCP UDP MTR DNS

Check TCP it-com-lake.check-host.eu:80

Checked Apr 21, 2026 01:35:46 UTC |

| Check again |

Location	Result	Time	IP Address
Albania, Tirana	ERROR	-	5.231.80.223
Australia, Sydney	ERROR	-	5.231.80.223
Bosnia and Herzegovina, Novi Travnik	ERROR	-	5.231.80.223
Bulgaria, Sofia	ERROR	-	5.231.80.223
Canada, Montreal	ERROR	-	5.231.80.223
Switzerland, Bern	ERROR	-	5.231.80.223
Chile, Santiago	ERROR	-	5.231.80.223
China, Hohhot	ERROR	-	5.231.80.223
Germany, Nuernberg	ERROR	-	5.231.80.223
Germany, Frankfurt am Main	ERROR	-	5.231.80.223
Germany, Frankfurt am Main	ERROR	-	5.231.80.223
Germany, Limburg	ERROR	-	5.231.80.223
Germany, Frankfurt am Main	ERROR	-	5.231.80.223
Germany, Duesseldorf	ERROR	-	5.231.80.223
Denmark, Glostrup Municipality	Connected	12.0 ms	5.231.80.223
Spain, Bilbao	ERROR	-	5.231.80.223
Finland, Helsinki	ERROR	-	5.231.80.223
Finland, Helsinki	ERROR	-	5.231.80.223
France, Gravelines	ERROR	-	5.231.80.223
France, Paris	Connected	9.0 ms	5.231.80.223
United Kingdom, London	ERROR	-	5.231.80.223
Georgia, Tbilisi	ERROR	-	it-com-lake.check-host.eu
Greece, Athens	ERROR	-	it-com-lake.check-host.eu
Hong Kong, Hong Kong	ERROR	-	5.231.80.223
Croatia, Zagreb	ERROR	-	5.231.80.223
Hungary, Budapest	Connected	15.0 ms	5.231.80.223
Indonesia, Jakarta	ERROR	-	5.231.80.223
Israel, Petach Tikwa	ERROR	-	5.231.80.223
Israel, Netanja	ERROR	-	5.231.80.223
India, New Delhi	ERROR	-	5.231.80.223
Iceland, Reykjavik (Miðborg)	ERROR	-	5.231.80.223
Italy, Como	ERROR	-	5.231.80.223
Kuwait, Kuwait City	ERROR	-	it-com-lake.check-host.eu
Lithuania, Pilaite	ERROR	-	5.231.80.223
Latvia, Riga	Connected	31.0 ms	5.231.80.223
Moldova, Chisinau	Connected	35.0 ms	5.231.80.223
Netherlands, Amsterdam	ERROR	-	5.231.80.223
Netherlands, Amsterdam	ERROR	-	5.231.80.223
Netherlands, Amsterdam	ERROR	-	5.231.80.223
Netherlands, Amsterdam	ERROR	-	5.231.80.223
Norway, Oslo	ERROR	-	5.231.80.223
Poland, Warsaw	Connected	15.0 ms	5.231.80.223
Romania, Bacău	ERROR	-	5.231.80.223
Romania, Bucharest	ERROR	-	5.231.80.223
Serbia, Belgrade	Connected	30.0 ms	5.231.80.223
Russia, St Petersburg	ERROR	-	5.231.80.223
Singapore, Singapore	ERROR	-	5.231.80.223
Turkey, Istanbul	ERROR	-	5.231.80.223
Taiwan, Taipei	ERROR	-	5.231.80.223
United States, Miami	ERROR	-	5.231.80.223
United States, Dallas	ERROR	-	5.231.80.223
United States, Kansas City	ERROR	-	5.231.80.223
United States, Dallas	ERROR	-	5.231.80.223
South Africa, Johannesburg	ERROR	-	5.231.80.223