What Is a Port Checker and How Does It Work?

Port Checker is a free online tool that checks a remote computer or device's Internet connectivity. It can be used to check for open ports or to Ping a remote server. This tool is also useful for testing Port Forwarding settings. The TCP Port Checker attempts to connect to the server and displays a success message on the screen if the connection is successful or if it receives a port open signal. You can't use this tools to check local ports in your computer.. To run this test, your computer or network device must be directly connected to the internet, or a port must be forwarded to the system if connected via a router.


What are the Prerequisites for port testing?

  • Checking ports is only possible if your computer is accessible via an public IP address.
  • When you are inside a subnet it is only possible with port forwarding.
  • Network access: You need access to the network where the port you want to test is located. This may require you to have physical access to the network, or you may need to remotely connect to the network using a VPN or other remote access tool.
  • Knowledge of the target port: You need to know the port number or protocol of the port you want to test. This information is usually available in documentation or online resources.
  • Firewall Access: Target port must be opened in Firewall.
port checker tool

Also, please note that in case you are testing open port for your local IP address i.e. if your Ip is similar to 192.168.1.xxx you are trying to check open port on internal IP and it is not going to work. If you are not sure about IP address and Port you shoud read more about [ Port Forwarding on Wikipedia ]

What is port forwarding?

Port Forwarding is a kind of special configuration on the router, which allows to redirect external requests (from the Internet) to computers or other devices on the local network. In fact it is a way to specify which local computer to send data and connection requests that arrive at a specific port on the router. We have three different ways we can do this:

  • Faux-DMZ: DMZ stands for Demilitarized Zone , which is a kind of network security configuration in which all incoming requests are sent to a specific computer in the network.
  • Port forwarding:
  • UPnP port forwarding: It is similar to Port Forwarding but in this case forwarding setting is done by a computer software which is residing on the Network. A very common example in the scenario is UPnP port forwarding setup done by Skype. Skype conference call is actually performed this way.

Let's say you have Minecraft Game Server or Apache Web server connected to the Internet via a router. All computers connected to the same router are on the same network, so will be able to connect to the server. However, outside of the Internet, connect to your server without port forwarding will not work. You must port forward Port 25565 for Minecraft and 80 for Apache to be accesible from Public internet. If your computer is connected to the Internet directly (without a router / router), then port forwarding is not required. All your open ports must be accessible from the Internet (of course, if you have a dedicated IP and these are accessible through your computer's Firewall ).

How to Test My Firewall

In case you have set up DMZ host and you want to test whether your firewall is effective of not, same can be verified by port checker tool. Use your public ip and test the ports which you have configured to block from your firewall.

What are ports? What are they used for?

In addition to these physical ports, computers also have virtual ports, which are used to communicate with other devices or services over a network using specific protocols. These virtual ports are identified by a port number, which is a unique number assigned to each type of service or protocol. For example, port 80 is used for HTTP (Hypertext Transfer Protocol), the protocol used to transfer web pages over the internet.

Ports are identified by numbers from 0 to 65535, inclusive. Any other port can not be opened, respectively, and check too. This limitation TCP / IP protocol. It is worth noting that the client program should always know the port to which it needs to connect to a remote server or another network device. For this reason, the most popular protocols reserved ports in the range from 0 to 1023. For example, carrying out surfing on the Internet, your browser connects to port 80 on a remote server that hosts the site. In response, the browser receives a set of data and code that downloads and displays a web page.

If you are not sure about the port numbers you do a port number lookup from standard database.

What are the different port numbers?

Out of the so many port numbers here are a few which are most frequently used.

FTP21File Transfer Protocol - File Transfer Protocol. Port for commands.
SSH22Secure SHell - "secure shell". Remote Management Protocol operating system.
Telnet23TerminaL Network. Protocol implementation text interface over the network.
SMTP25Simple Mail Transfer Protocol - Simple Mail Transfer Protocol.
WHOIS43"Who is". Protocol obtaining the registration of ownership of domain names and IP addresses
DNS53Domain Name System - Domain Name System.
DHCP67Dynamic Host Configuration Protocol - Dynamic Host Configuration Protocol. Dynamic IP
TFTP69Trivial File Transfer Protocol - a simple file transfer protocol.
HTTP / Web80HyperText Transfer Protocol - hypertext transfer protocol.
POP3110Post Office Protocol Version 3 - receive e-mail protocol, version 3
SFTP115SSH File Transfer Protocol. Secure data transmission protocol.
IMAP143Internet Message Access Protocol. Application-level protocol for accessing e-mail.
SNMP161Simple Network Management Protocol - Simple Network Management Protocol. Device Management.
HTTPS443HyperText Transfer Protocol Secure) - protocol HTTP, which supports encryption.
LPD515Line Printer Daemon. Remote printing protocol on the printer.
IMAP SSL993Protocol IMAP, supports SSL encryption.
POP3 SSL995POP3 protocol supports SSL encryption.
SOCKS1080SOCKet Secure. Receiving protocol secure anonymous access.
Proxy3128Currently the port often used proxies.
MySql3306Mysql database
RDP3389Remote Desktop Protocol - Remote Desktop for Windows.
PostgreSql5432Postgres Database
VNC5900Virtual Network Computing - a system of remote access to the desktop computer.
TeamViewer5938TeamViewer - Remote control system for ensuring your computer and data exchange.
HTTP / Web8080Alternate port for the HTTP protocol. Sometimes used proxies.
Minecraft25565Minecraft Server Port

Can I check Blocked Ports using Port Checker Tool ?

Yes, you can check for open ports as well as blocked ports in a Computer or Server Environment. While testing a specific port if result is returned as "Closed" means that particular port is blocked or inaccessible.

Command to test open ports in MAC, Windows or Linux computers

If you using a Windows or Linux machine, you can easily find open ports or ports which are in use using below commands :

Windows : Start → "cmd" → Run as Administrator → "netstat -bn"
Linux : a In the terminal, run the command: "ss -tln"
MAC : lsof -iTCP -sTCP:LISTEN -n -P

How to close an open port?

First of all it is necessary to remove the cause - a running program or service that opened the port; it is necessary to close / stop. If the open port reason is not clear - Antivirus scan your computer, delete the extra port forwarding rules on the router and set the advanced firewall (Firewall).

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