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Scan Common Ports
FTP - 21 SSH - 22 SMTP - 25 HTTP - 80 HTTP - 8080 RDP - 3389 POP3 - 110

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.

Why do you need to check open ports?

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Check open ports is possible if your computer's current external IP address. More about this you can ask your ISP. It is worth considering that if your computer is connected to the Internet, instead of directly through the router (the router), the test results are exactly to the router. Check the port status for the computer inside a subnet is possible only with port forwarding.

Frequently Used Ports

21FTP File Transfer Protocol - File Transfer Protocol. Port for commands.
22SSHSecure SHell - "secure shell". Remote Management Protocol operating system.
23telnetTErminaL NETwork. Protocol implementation text interface over the network.
25SMTPSimple Mail Transfer Protocol - Simple Mail Transfer Protocol.
43WHOIS"Who is". Protocol obtaining the registration of ownership of domain names and IP addresses
53DNSDomain Name System - Domain Name System.
67DHCPDynamic Host Configuration Protocol - Dynamic Host Configuration Protocol. Dynamic IP
69TFTPTrivial File Transfer Protocol - a simple file transfer protocol.
80HTTP / WebHyperText Transfer Protocol - hypertext transfer protocol.
110POP3Post Office Protocol Version 3 - receive e-mail protocol, version 3
115SFTPSSH File Transfer Protocol. Secure data transmission protocol.
143IMAPInternet Message Access Protocol. Application-level protocol for accessing e-mail.
161SNMPSimple Network Management Protocol - Simple Network Management Protocol. Device Management.
443HTTPSHyperText Transfer Protocol Secure) - protocol HTTP, which supports encryption.
515LPDLine Printer Daemon. Remote printing protocol on the printer.
993IMAP SSLProtocol IMAP, supports SSL encryption.
995POP3 SSLPOP3 protocol supports SSL encryption.
1080SOCKSSOCKet Secure. Receiving protocol secure anonymous access.
3128ProxyCurrently the port often used proxies.
3389RDPRemote Desktop Protocol - Remote Desktop for Windows.
5900VNCVirtual Network Computing - a system of remote access to the desktop computer.
5938TeamViewerTeamViewer - Remote control system for ensuring your computer and data exchange.
8080HTTP / WebAlternate port for the HTTP protocol. Sometimes used proxies.

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.

port checker - port forwarding

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).

Read more about port forwarding at wikipedia [ Port Forwarding on Wikipedia ]

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 also be verified by port checker tool. Use your publich ip and test the ports which you have configured to block from your firewall.

What are ports? What are they used for?

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."

Which port numbers can opened?

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.

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).

Command to check open port in your computer

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"

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