TCP Port Checker
Test TCP handshake connectivity on any port (1–65535) from external vantage points. Determine whether firewall rules allow inbound traffic.
Best solution
Network diagnostic: TCP Port Checker; SYN/ACK Handshake Latency.
No measurement yet. This checks from Globalping probes, not from your computer. No continuous monitoring.
Keep fast calculators and daily tools pinned right to your desktop.
Methodology & calculation rule
Initiates a 3-packet TCP SYN probe to the destination host and port, recording whether SYN/ACK replies or timeouts occur.
Network observations execute bounded requests to public measurement backends (ipify, Google Public DNS, Globalping, or Cloudflare). Measurements distinguish local client configuration from external internet reachability.
No browsing history, private tokens, or credentials are captured. Results are snapshots of external probe vantage points at the recorded observation timestamp.
Real-World Context & Technical Standards
TCP 3-Way Handshake (SYN, SYN-ACK, ACK)
A TCP port check verifies whether the destination endpoint responds with a SYN-ACK packet to complete connection establishment, confirming that a listening socket is actively bound to the port.
Open vs. Filtered (Stealth) States
An open port returns SYN-ACK; a closed port returns RST (Reset); an administrative firewall drops the probe silently without responding, resulting in a connection timeout.
Well-Known, Registered, and Dynamic Ports
Ports 0–1023 are IANA well-known privileged service ports (e.g. 80 for HTTP, 443 for HTTPS, 22 for SSH); ports 1024–49151 are registered user ports; and 49152–65535 are ephemeral dynamic ports.
Related network diagnostic tools
| Tool | Metric | Scope |
|---|---|---|
| What Is My IP Address? | Diagnostic | what is my ip address |
| IP Address Lookup | Diagnostic | ip address lookup |
| Remote Ping Test | Diagnostic | ping test |
| DNS Lookup | Diagnostic | dns lookup |
| Is It Down? | Diagnostic | is it down |
Frequently Asked Questions
What are the most commonly checked TCP ports?
Port 80 (HTTP), Port 443 (HTTPS), Port 22 (SSH), Port 25/587 (SMTP email), and Port 3389 (RDP) are the standard ports verified during service deployments.
Does an open port mean the application is operating correctly?
Not necessarily. An open port confirms that the TCP 3-way handshake succeeded at the transport layer, but the application daemon behind it could still encounter internal errors or fail authentication.