Whois Ping is offering Port Checker which is a simple and free online tool to check open ports on your computer/device, It is mostly useful in testing port forwarding setup on a machine. For Example, if you are facing connection issue with a program (email, IM client etc) then it may be possible that the port required by the application is getting blocked by firewall or ISP(Internet Service Provider). In such cases, this tool might be helpful to you in diagnosing the issue. It could also be useful for security reasons, in case you are worried whether a particular port is open or closed.
Port numbers ranges from 1 to 65535, out of which well known ports are pre-defined as convention by IANA.
If you're looking for a full list of port numbers check out this wikipedia page.
Port forwarding or port mapping involves translating the address (or port number to a new destination), accepting the packets and forwarding it (using routing table). It's typically used in connecting remote computers to specific programs running on computer (in a private LAN (Local Area Network)). For example : running a public server (HTTP, port 80) on a computer in a private LAN or granting SSH access to a specific computer in a private LAN etc. Read More on Wikipedia.
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