Port Checker is an online tool which checks a remote computer or device accessibility from the Internet. It can be used to check ports on a remote server. TCP port checker tries to establish TCP connection from our server and if the connection is successful, You should be able to see it.
Open port checking is only possible if your computer is accessible by external/public IP address. It is worth considering that if your computer is connected to the Internet, through the router , the test results are exactly to the router. Testing the port status for the computer inside a subnet is only possible with port forwarding.
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 ]
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.
Let's say you have a home game or a 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. If your computer is connected to the Internet directly (without a router / router), then perform port forwarding is required. All your open ports must be accessible from the Internet (of course, if you have a dedicated IP).
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 publich ip and test the ports which you have configured to block from your firewall.
Ports that virtual address on your computer or network device which enables it communicate with other computer or devices. If a program or service plans to work with the network, it opens the port with a unique number, through which it can work with remote clients / servers. In human language it would sound something like this: "I, the server program, open port 1234. If the network cable will come with data port number 1234 - that to me."
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.
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).
|21-FTP||File Transfer Protocol - File Transfer Protocol. Port for commands.|
|22-SSH||Secure SHell - "secure shell". Remote Management Protocol operating system.|
|23-telnet||TErminaL NETwork. Protocol implementation text interface over the network.|
|25-SMTP||Simple Mail Transfer Protocol - Simple Mail Transfer Protocol.|
|43-WHOIS||"Who is". Protocol obtaining the registration of ownership of domain names and IP addresses|
|53-DNS||Domain Name System - Domain Name System.|
|67-DHCP||Dynamic Host Configuration Protocol - Dynamic Host Configuration Protocol. Dynamic IP|
|69-TFTP||Trivial File Transfer Protocol - a simple file transfer protocol.|
|80-HTTP / Web||HyperText Transfer Protocol - hypertext transfer protocol.|
|110-POP3||Post Office Protocol Version 3 - receive e-mail protocol, version 3|
|115-SFTP||SSH File Transfer Protocol. Secure data transmission protocol.|
|143-IMAP||Internet Message Access Protocol. Application-level protocol for accessing e-mail.|
|161-SNMP||Simple Network Management Protocol - Simple Network Management Protocol. Device Management.|
|443-HTTPS||HyperText Transfer Protocol Secure) - protocol HTTP, which supports encryption.|
|515-LPD||Line Printer Daemon. Remote printing protocol on the printer.|
|993-IMAP SSL||Protocol IMAP, supports SSL encryption.|
|995-POP3 SSL||POP3 protocol supports SSL encryption.|
|1080-SOCKS||SOCKet Secure. Receiving protocol secure anonymous access.|
|3128-Proxy||Currently the port often used proxies.|
|3389-RDP||Remote Desktop Protocol - Remote Desktop for Windows.|
|5900-VNC||Virtual Network Computing - a system of remote access to the desktop computer.|
|5938-TeamViewer||TeamViewer - Remote control system for ensuring your computer and data exchange.|
|8080-HTTP / Web||Alternate port for the HTTP protocol. Sometimes used proxies.|
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"