Port Scan

Please enter Host or IP to Scan
	Example: google.com or 74.125.226.82

What is Port Scanning?

Port scan lets you check to see if ports on a host or at a specific IP address are responding. This is useful for checking the status for remote servers or for your local machine. For security purposes, many servers and devices will block individual ports, ranges of ports or ports designated for certain types of protocols. Blocking ports, however, is a double - edged sword - while you may block users and other agents from unauthorized access to your network or device, you may also be hindering protocols or clients (such as email, HTTP, or FTP) from accessing your machine.

Understanding Network Ports

If an IP address is like a server or computer’s phone number, a port is like an extension that’s dedicated to a certain department. Ideally, each application or protocol uses a designated port. For example, web browsers exchange data via port 80, which is reserved for HTTP connections. Mail servers send mail using the Simple Mail Transfer Protocol (SMTP) port, which is usually 25. By using port 25 as the standard port for receiving mail, servers know to “listen” at that port for any incoming traffic.

If a particular port is blocked or the server is not listening at the port, data and requests to it will go unanswered. This is just like if you dialed an extension that didn’t exist - no one would be there to answer it.

What is Port Scanning used for?

Port scanning helps you identify open ports through which you can communicate with a server or remote computer. This can also help you troubleshoot your own servers or network devices. For example, if your web server isn’t responding on port 80, then clearly there is something wrong with your network configuration - perhaps a firewall is set up incorrectly, or a name server is misconfigured.

Port scanning is also helpful for setting up applications which may not have designated ports, such as peer - to - peer file sharing applications, online games and web services. If a particular application is having trouble reaching the Internet, try running a port scan on your own machine to see which ports are open. Then, change the port for the program to listen on in your application preferences.

You can also use a port scan on a remote web server in order to determine which services are available.

Common port numbers include:

Port 21 (FTP) - File Transfer

Port 23 (Telnet)

Port 25 (SMTP) - Email

Port 80 (HTTP) - Web browsers

Port 110 (POP3) - Email

Port 1433 (MSSQL) SQL Server Database

Port 3306 (MySQL) - Databases

Port 8080 (Webcache) - Firewall Access

Note: Servers can allow or disallow access at ports based on the IP address of the requester. For example, your company may allow you to access your company’s network from your home office, but disallow access if you try to connect from a public wireless network at a cafe or library.

Also note that your ISP may block certain ports. For example, port 25 is often blocked to prevent spammers from sending outgoing emails from a dynamic IP.