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.

cn-hoh-alibaba.check-host.eu:80 のレポート

Name: Check-Host cn-hoh-alibaba.check-host.eu:80 TCP ポート疎通テスト
Author: Check-Host

Info Ping HTTP TCP UDP MTR DNS

TCP チェック cn-hoh-alibaba.check-host.eu:80

Apr 22, 2026 16:36:37 UTC に確認 |

| 再チェック |

拠点	結果	応答時間	IP アドレス
Albania, Tirana	ERROR	-	39.104.200.240
Australia, Sydney	ERROR	-	39.104.200.240
Bosnia and Herzegovina, Novi Travnik	ERROR	-	39.104.200.240
Bulgaria, Sofia	ERROR	-	39.104.200.240
Canada, Montreal	ERROR	-	39.104.200.240
Switzerland, Bern	ERROR	-	39.104.200.240
Chile, Santiago	ERROR	-	39.104.200.240
China, Hohhot	ERROR	-	39.104.200.240
Germany, Nuernberg	ERROR	-	39.104.200.240
Germany, Frankfurt am Main	ERROR	-	39.104.200.240
Germany, Frankfurt am Main	ERROR	-	39.104.200.240
Germany, Limburg	ERROR	-	39.104.200.240
Germany, Frankfurt am Main	ERROR	-	39.104.200.240
Germany, Duesseldorf	ERROR	-	39.104.200.240
Denmark, Glostrup Municipality	Connected	12.0 ms	39.104.200.240
Spain, Bilbao	ERROR	-	39.104.200.240
Finland, Helsinki	ERROR	-	39.104.200.240
Finland, Helsinki	ERROR	-	39.104.200.240
France, Gravelines	ERROR	-	39.104.200.240
France, Paris	Connected	60.0 ms	39.104.200.240
United Kingdom, London	ERROR	-	39.104.200.240
Georgia, Tbilisi	ERROR	-	cn-hoh-alibaba.check-host.eu
Greece, Athens	ERROR	-	cn-hoh-alibaba.check-host.eu
Hong Kong, Hong Kong	ERROR	-	39.104.200.240
Croatia, Zagreb	ERROR	-	39.104.200.240
Hungary, Budapest	Connected	16.0 ms	39.104.200.240
Indonesia, Jakarta	ERROR	-	39.104.200.240
Israel, Petach Tikwa	ERROR	-	39.104.200.240
Israel, Netanja	ERROR	-	39.104.200.240
India, New Delhi	ERROR	-	39.104.200.240
Iceland, Reykjavik (Miðborg)	ERROR	-	39.104.200.240
Italy, Como	ERROR	-	39.104.200.240
Kuwait, Kuwait City	ERROR	-	cn-hoh-alibaba.check-host.eu
Lithuania, Pilaite	ERROR	-	39.104.200.240
Latvia, Riga	Connected	31.0 ms	39.104.200.240
Moldova, Chisinau	Connected	36.0 ms	39.104.200.240
Netherlands, Amsterdam	ERROR	-	39.104.200.240
Netherlands, Amsterdam	ERROR	-	39.104.200.240
Netherlands, Amsterdam	ERROR	-	39.104.200.240
Netherlands, Amsterdam	ERROR	-	39.104.200.240
Norway, Oslo	ERROR	-	39.104.200.240
Poland, Warsaw	Connected	20.0 ms	39.104.200.240
Romania, Bacău	ERROR	-	39.104.200.240
Romania, Bucharest	ERROR	-	39.104.200.240
Serbia, Belgrade	Connected	32.0 ms	39.104.200.240
Singapore, Singapore	ERROR	-	39.104.200.240
Turkey, Istanbul	ERROR	-	39.104.200.240
Taiwan, Taipei	ERROR	-	39.104.200.240
United States, Miami	ERROR	-	39.104.200.240
United States, Dallas	ERROR	-	39.104.200.240
United States, Kansas City	ERROR	-	39.104.200.240
United States, Dallas	ERROR	-	39.104.200.240
South Africa, Johannesburg	ERROR	-	39.104.200.240