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 time.nist.gov:123

Info Ping HTTP TCP UDP MTR DNS

Check TCP time.nist.gov:123

Checked Apr 21, 2026 04:33:14 UTC |

| Check again |

Location	Result	Time	IP Address
Albania, Tirana	ERROR	-	132.163.97.3
Australia, Sydney	ERROR	-	132.163.96.1
Bosnia and Herzegovina, Novi Travnik	ERROR	-	132.163.96.4
Bulgaria, Sofia	ERROR	-	132.163.96.4
Canada, Montreal	ERROR	-	132.163.96.3
Switzerland, Bern	ERROR	-	132.163.97.6
Chile, Santiago	ERROR	-	132.163.97.4
China, Hohhot	ERROR	-	132.163.97.1
Germany, Nuernberg	ERROR	-	132.163.96.1
Germany, Frankfurt am Main	ERROR	-	132.163.97.2
Germany, Frankfurt am Main	ERROR	-	132.163.96.6
Germany, Limburg	ERROR	-	132.163.96.6
Germany, Frankfurt am Main	ERROR	-	132.163.96.2
Germany, Duesseldorf	ERROR	-	132.163.97.3
Denmark, Glostrup Municipality	ERROR	-	132.163.97.4
Spain, Bilbao	ERROR	-	132.163.97.3
Finland, Helsinki	ERROR	-	132.163.97.6
Finland, Helsinki	ERROR	-	129.6.15.25
France, Gravelines	ERROR	-	132.163.96.3
France, Paris	ERROR	-	132.163.96.6
United Kingdom, London	ERROR	-	129.6.15.25
Georgia, Tbilisi	ERROR	-	time.nist.gov
Greece, Athens	ERROR	-	time.nist.gov
Hong Kong, Hong Kong	ERROR	-	132.163.96.6
Croatia, Zagreb	ERROR	-	132.163.96.2
Hungary, Budapest	ERROR	-	132.163.97.3
Indonesia, Jakarta	ERROR	-	132.163.96.2
Israel, Petach Tikwa	ERROR	-	132.163.97.1
Israel, Netanja	ERROR	-	132.163.97.1
India, New Delhi	ERROR	-	132.163.97.3
Iceland, Reykjavik (Miðborg)	ERROR	-	129.6.15.25
Italy, Como	ERROR	-	132.163.97.2
Kuwait, Kuwait City	ERROR	-	time.nist.gov
Lithuania, Pilaite	ERROR	-	132.163.96.4
Latvia, Riga	ERROR	-	129.6.15.25
Moldova, Chisinau	ERROR	-	132.163.96.1
Netherlands, Amsterdam	ERROR	-	132.163.97.6
Netherlands, Amsterdam	ERROR	-	132.163.96.2
Netherlands, Amsterdam	ERROR	-	129.6.15.26
Netherlands, Amsterdam	ERROR	-	132.163.96.3
Norway, Oslo	ERROR	-	132.163.97.6
Poland, Warsaw	ERROR	-	132.163.97.4
Romania, Bacău	ERROR	-	132.163.96.4
Romania, Bucharest	ERROR	-	132.163.96.2
Serbia, Belgrade	ERROR	-	129.6.15.27
Russia, St Petersburg	ERROR	-	129.6.15.25
Singapore, Singapore	ERROR	-	129.6.15.25
Turkey, Istanbul	ERROR	-	132.163.96.2
Taiwan, Taipei	ERROR	-	132.163.96.2
United States, Miami	ERROR	-	132.163.97.1
United States, Dallas	ERROR	-	132.163.97.2
United States, Kansas City	ERROR	-	132.163.97.2
United States, Dallas	ERROR	-	132.163.96.2
South Africa, Johannesburg	ERROR	-	132.163.96.3