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8.8.8.8:80
1.1.1.1:443
192.168.0.1:22
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$ checkhost monitor --type tcp port --interval 30s
Need continuous tcp port monitoring?
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About
TCP Port Checker — Test Open Ports From 15 Locations
A TCP port check tests whether a specific port on a server is open and accepting connections. TCP (Transmission Control Protocol) is the foundation of most internet services — every web server, database, email server, and application server listens on specific TCP ports. Common ports include: 80 (HTTP), 443 (HTTPS), 22 (SSH), 21 (FTP), 25/587 (SMTP email), 3306 (MySQL), 5432 (PostgreSQL), 6379 (Redis), 27017 (MongoDB), 3389 (RDP), and 8080/8443 (alternative HTTP). CheckHost tests TCP connectivity from 15 global locations, helping you verify firewall rules work correctly worldwide, detect ports blocked by ISPs or country-level firewalls, confirm your services are accessible from different regions, and troubleshoot connection issues. Results show whether each port is Open (connection successful), Closed (connection actively refused), or Filtered (no response — typically firewalled).
Usage
How to Check TCP Ports With CheckHost
Enter the host and port in the format host:port (e.g., example.com:443, 192.168.1.1:22, my-server.com:3306).
Select 'TCP' from the tool tabs and click Check to test connectivity from 15 locations.
Results show the connection status from each location: successful connections display the response time, failed ones show the error.
If results vary between locations, some networks or countries may be blocking that port. Check your firewall rules and hosting provider's network policies.
For security: ports that should only be accessible from specific IPs (databases, SSH, admin panels) should show as filtered/closed from public testing locations.
FAQ
Frequently Asked Questions
What are the most common TCP ports?
80 = HTTP (web), 443 = HTTPS (secure web), 22 = SSH (remote access), 21 = FTP (file transfer), 25 = SMTP (email sending), 587 = SMTP submission, 993 = IMAPS (email retrieval), 3306 = MySQL, 5432 = PostgreSQL, 6379 = Redis, 27017 = MongoDB, 3389 = RDP (Windows remote desktop), 8080 = HTTP alternate, 8443 = HTTPS alternate.
What's the difference between Open, Closed, and Filtered?
Open: a service is listening and accepted the TCP connection (SYN → SYN-ACK). Closed: the port actively sent a RST (reset) packet — the server is reachable but no service is listening on that port. Filtered: no response at all — usually means a firewall is silently dropping packets. Filtered is the most secure state for ports you don't want accessible publicly.
Should I worry about open ports?
Only ports running services should be open. Every open port is a potential attack surface. Best practices: close all ports you don't need, use firewalls to restrict access to trusted IPs for sensitive ports (SSH, databases, admin panels), keep services updated to patch vulnerabilities, use non-standard ports for sensitive services (e.g., SSH on 2222 instead of 22).
Why is a port open from some locations but not others?
This typically means geo-IP firewall rules are in place, certain ISPs or countries block specific ports, your hosting provider restricts access from certain regions, or a DDoS protection service is filtering traffic by geography. This can be intentional (security) or a problem to fix.