How to Check If a Port Is Open

Published March 7, 2026 · 5 min read

You're trying to set up a game server, access a remote machine, or troubleshoot why an app can't connect. The first question is usually: is the port actually open? Here's everything you need to know about checking ports and what the results mean.

What Are Ports?

If an IP address is like a street address, a port is like a specific door in the building. Each networked device has 65,535 available ports, and different services use different ports to communicate. When you visit a website, your browser connects to port 443 (HTTPS). When you send an email, your mail client connects to port 587 (SMTP).

A port can be in one of three states:

• Open — a service is listening and accepting connections
• Closed — the port is reachable but no service is listening
• Filtered — a firewall is blocking the connection, so you can't tell if it's open or closed

Common Port Numbers

These are the ports you'll encounter most often:

• 21 — FTP (file transfer)
• 22 — SSH (secure shell)
• 25 — SMTP (outgoing email)
• 53 — DNS (domain name resolution)
• 80 — HTTP (unencrypted web)
• 443 — HTTPS (encrypted web)
• 993 — IMAPS (incoming email, encrypted)
• 3306 — MySQL (database)
• 3389 — RDP (Windows remote desktop)
• 5900 — VNC (remote screen sharing)
• 8080 — HTTP alternate (often used for web admin panels)

How to Check a Port

From your iPhone

Open PingKit and use the Port Scanner tool. Enter the hostname or IP address and specify the port or range of ports you want to check. PingKit will test each port and tell you whether it's open, closed, or filtered, along with the service name associated with each open port.

What the results mean

• Port is open — a service is running and reachable. If this is unexpected, investigate what's running on that port
• Port is closed — the host is reachable but nothing is listening on that port. The service either isn't running or is configured to use a different port
• Port is filtered — a firewall is silently dropping your packets. The port might be open behind the firewall, but you can't reach it from your current network

Common Scenarios

Checking if your server is accessible

If you're running a web server, game server, or any other service, you need to make sure the port is reachable from outside your network. Scan the port from your phone's cellular connection (turn off WiFi) to test from an external perspective. If the port shows as filtered, you likely need to set up port forwarding on your router.

Verifying a firewall is working

After configuring firewall rules, scan the relevant ports to confirm they're actually blocked. A port that should be closed but shows as open means your firewall rules aren't applied correctly.

Troubleshooting connection issues

If an app can't connect to a service, scan the service's port to determine if it's a network issue (port filtered/closed) or an application issue (port open but app still can't connect). This saves a lot of time narrowing down where the problem is.

Port Scanning and Security

Every open port is a potential entry point for attackers. Good security practice means:

• Close ports you don't need — if a service isn't in use, stop it
• Keep services updated — open ports running outdated software are the most common attack vector
• Use non-standard ports — moving SSH from port 22 to a random high port (e.g., 49222) reduces automated attacks
• Use a firewall — only allow connections to ports that need to be publicly accessible

Port Forwarding

If you need a port to be accessible from outside your home network (e.g., for a game server or remote access), you'll need to set up port forwarding on your router. This tells your router to direct incoming traffic on a specific port to a specific device on your local network.

After setting up a port forward, use PingKit's Port Scanner from cellular data to verify it's working. If the port still shows as filtered, double-check that your ISP isn't blocking it — some ISPs block common ports like 80 and 25 on residential connections.