what is tcp/ip port scanning and what exactly can a layman achieve with it?

Answer 1

TCP/IP Port Scanning is when you pass different kinds of requests to an IP address to determine if anything reponds from that IP. You can determine what services are running on that remote IP based on what port generates a response. Attackers use this to find out what "doorways" to the remote computer are open, and then use other tactics to try and gain access to that remote computer through that port. I can't think of a single reason for a layman to use this technique, though.

Answer 2

There are 65,536 ports used by the TCP/IP protocol. Ports provide an endpoint to a logical connection between two computers. The first 1025 ports, 0 through 1024, are termed "well-known ports." These include such ports as 20 & 21, for FTP, 25 for SMTP, 80 for HTTP, 110 for POP3, and so on. TCP/IP port scanning is using a program to scan through some or all of the 65,536 ports to see which ports are open and actively listening for requests. This can be useful for administrators trying to determine if there are any open ports that need to be secured on hosts. By the same token, it can be used by people looking for open ports to be exploited. It can also be used to troubleshoot problems; for example, if you're trying to figure out why a webserver isn't working and a port scan shows that port 80 is closed, then you know immediately what the problem is (or at least, where to start).

Answer 3

the above answer is correct. There is a command called netstat which you can run from the command prompt, this will tell you what ports are currently in use and what machine is connected to yours and what port number is being used for the connection.