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.

check-host.cc:80 のレポート

Name: Check-Host check-host.cc: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 check-host.cc:80

Apr 21, 2026 00:16:08 UTC に確認 |

| 再チェック |

拠点	結果	応答時間	IP アドレス
Albania, Tirana	Connected	58.0 ms	34.36.183.77
Australia, Sydney	Connected	1.0 ms	34.36.183.77
Bosnia and Herzegovina, Novi Travnik	Connected	47.0 ms	34.36.183.77
Bulgaria, Sofia	Connected	26.0 ms	34.36.183.77
Canada, Montreal	Connected	1.0 ms	34.36.183.77
Switzerland, Bern	Connected	2.0 ms	34.36.183.77
Chile, Santiago	Connected	1.0 ms	34.36.183.77
China, Hohhot	Connected	298.0 ms	34.36.183.77
Germany, Nuernberg	Connected	4.0 ms	34.36.183.77
Germany, Frankfurt am Main	Connected	1.0 ms	34.36.183.77
Germany, Frankfurt am Main	Connected	1.0 ms	34.36.183.77
Germany, Limburg	Connected	1.0 ms	34.36.183.77
Germany, Frankfurt am Main	Connected	1.0 ms	34.36.183.77
Germany, Duesseldorf	Connected	5.0 ms	34.36.183.77
Denmark, Glostrup Municipality	Connected	12.0 ms	34.36.183.77
Spain, Bilbao	Connected	36.0 ms	34.36.183.77
Finland, Helsinki	Connected	6.0 ms	34.36.183.77
Finland, Helsinki	Connected	12.0 ms	34.36.183.77
France, Gravelines	Connected	5.0 ms	34.36.183.77
France, Paris	Connected	10.0 ms	34.36.183.77
United Kingdom, London	Connected	6.0 ms	34.36.183.77
Georgia, Tbilisi	ERROR	-	check-host.cc
Greece, Athens	ERROR	-	check-host.cc
Hong Kong, Hong Kong	Connected	4.0 ms	34.36.183.77
Croatia, Zagreb	Connected	23.0 ms	34.36.183.77
Hungary, Budapest	Connected	29.0 ms	34.36.183.77
Indonesia, Jakarta	Connected	15.0 ms	34.36.183.77
Israel, Petach Tikwa	Connected	3.0 ms	34.36.183.77
Israel, Netanja	Connected	4.0 ms	34.36.183.77
India, New Delhi	Connected	1.0 ms	34.36.183.77
Iceland, Reykjavik (Miðborg)	Connected	58.0 ms	34.36.183.77
Italy, Como	Connected	19.0 ms	34.36.183.77
Kuwait, Kuwait City	ERROR	-	check-host.cc
Lithuania, Pilaite	Connected	39.0 ms	34.36.183.77
Latvia, Riga	Connected	31.0 ms	34.36.183.77
Moldova, Chisinau	Connected	35.0 ms	34.36.183.77
Netherlands, Amsterdam	Connected	2.0 ms	34.36.183.77
Netherlands, Amsterdam	Connected	4.0 ms	34.36.183.77
Netherlands, Amsterdam	Connected	2.0 ms	34.36.183.77
Netherlands, Amsterdam	Connected	3.0 ms	34.36.183.77
Norway, Oslo	Connected	12.0 ms	34.36.183.77
Poland, Warsaw	Connected	15.0 ms	34.36.183.77
Romania, Bacău	Connected	33.0 ms	34.36.183.77
Romania, Bucharest	Connected	35.0 ms	34.36.183.77
Serbia, Belgrade	Connected	30.0 ms	34.36.183.77
Russia, St Petersburg	Connected	5.0 ms	34.36.183.77
Singapore, Singapore	Connected	1.0 ms	34.36.183.77
Turkey, Istanbul	Connected	32.0 ms	34.36.183.77
Taiwan, Taipei	Connected	5.0 ms	34.36.183.77
United States, Miami	ERROR	-	34.36.183.77
United States, Dallas	Connected	18.0 ms	34.36.183.77
United States, Kansas City	Connected	26.0 ms	34.36.183.77
United States, Dallas	Connected	2.0 ms	34.36.183.77
South Africa, Johannesburg	Connected	0.0 ms	34.36.183.77