- 21 FTP
- 22 SSH
- 23 TELNET
- 25 SMTP
- 53 DNS
- 80 HTTP
A port is a physical docking point that can be used to connect an external device to the computer. It may also be a programmatic docking point from which knowledge flows to the computer or over the Internet from a program.
A network port that is provided by the Transport Layer protocols of the Internet Protocol Suite, such as Transmission Control Protocol (TCP) and User Diagram Protocol (UDP) is a number that serving endpoint communication between two computers.
Each networking mechanism or system uses a particular port of the network to transmit and receive data. That means listening for incoming packets whose destination port matches the port number, and/or transmitting outgoing packets whose source port is matched to that port number. Processes can use multiple ports in the network to receive and send data.
The port numbers that range from 0 to 1023 are known as well-known port numbers. Well-known port numbers, such as FTP and Telnet, are assigned to common server processes. They are referenced by system processes that provide widely used network service types. The Internet Assigned Numbers Authority (IANA) assigns and registers the relevant port numbers.
Port forwarding is also known as tunneling, is the behind-the-scenes process of intercepting data traffic headed for a computer’s IP/port combination and redirecting it to a different IP and/or port. A program that’s running on the destination computer usually causes the redirection, but sometimes it can also be an intermediate hardware component, such as a router, proxy server or firewall.
It begins with the packets that get created when you send a data request over the Internet.
Normally, a network router will examine an IP packet’s header and send it to a linked and appropriate interface, which in turn sends the data to the information in the header for a destination.
But the intercepting program (or device) reads the packet header in port forwarding, notices the destination, then rewrites the header information and sends it to another machine which is different from the one intended.
The secondary host destination may be a different IP address using the same port, a different port at the same IP address or a completely different combination of the two.
Checking Open Ports
If you want to check the open ports then you can use our free online Port Checker tool. Port Checker checks the accessibility of a remote server or a computer from the internet. It does so by establishing a connection to the given IP and port. If the connection is successfully established then it means that a port is open.
Port checking for a computer or server is only possible if it is accessible by a public IP address. Local IP addresses such as 192.168.xxx.xxx will not work.
Close an Open Port
If you want to close an open port then you must first remove the program or service that opened the port. It is important that you close or stop that program or service and it will result in the closure of that port. Let’s say you have a port 5938 opened and it is caused by TeamViewer. So, to close this port you must first remove the program, i.e TeamViewer and it will close the port.
If the program or service is unknown then you can use an antivirus to scan your computer and then delete the extra port-forwarding rules.