Is My Port Open?

This is a free tool you can use to check if a specific port on your computer or device is open to the public or not. This is often being used to test if port forwarding is set up on your machine. For certain software, a specific port needs to be accessible to the public.

Popular Ports

A well-known port is the one where every protocol of the network service has a specific port assigned to it. Here is a list of well-known TCP/UDP ports.

The FTP (Default data), one of the more common protocols, has a port number of 20. The FTP (Connection dialog, control) has a port number of 21, on the other hand. Here is a look at some of the other common protocols, and their port numbers.

• Telnet 23
• SMTP 25
• DNS 53
• DHCP BOOTP Server 67
• DHCP BOOTP Client 68
• TFTP 69
• Gopher 70
• HTTP 80
• POP3 110
• NNTP 119
• NetBIOS Session Service 139
• Internet Message Access Protocol
  (IMAP), version 2 143

What Is Port Checker

Port checkers are free online tools to check open ports on your computer/device. The port checkers help check port forwarding settings on a machine. For example, if you have any connection issue with any program, its port could be getting blocked by a firewall or ISP. Therefore, a port checker will help you understand if the port is getting blocked for the communication or is open for it. It also helps with the security, as an unwanted open port can be unsafe for your computer. 

Port Definition

Port is a communication endpoint in a networking system. Any connection, physical or wireless, is terminated at a port of a hardware device. In an operating system, a port is a logical construct that resembles a specific process or any network service. Port numbers are 16-bit unsigned numbers that they are identified with. The number is a combination of its protocol and address. The protocols that use port numbers include Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP). 

Port numbers usually have two ranges, well-known and registered. The ports of Internet services with a specific port assigned to them are well-known ports. For example, port 25 is for SMTP, and port 80 is for HTTP. Registered ports are the temporary ones for the clients that vary each time someone uses them. They are also known as ephemeral ports because they only function for a short period. The range of well-known ports is from 1-1023, and registered ports are 1024-65535.

Open Ports vs. Closed Ports

A port that can accept packets of information in network communication is an open port. A closed port is the one that rejects connections or ignores any packets that are directed at it. However, an open port is not enough to establish a communication channel. 

The port also needs to have an application configured on it, that can accept and process the incoming packets. If there is no application listening on that port, it will reject any of the incoming packets. A port can also be closed with a firewall. A firewall shows the port as closed for every packet, except the ones for which are configured. 

What Is Port Forwarding?

Port forwarding is a way of rerouting the data meant for a specific IP/port combination to another computer's IP/port combination. A program running on the host usually manages the redirection, but it can also happen due to a firewall, router, or proxy server.

Usually, the host recognizes the header of the IP packet and sends it to an interface. This interface sends the data to the destination that's mentioned in the header. But in port forwarding, the interception application reads the header, makes a note of the destination, and sends the packet to another computer after rewriting the header. The second host can have a different IP address on the same port, can be a different port on the same IP, or have a combination of the two.