Technical,
The IANA port lists identify known uses for TCP/UDP ports. "The Well Known Ports are those from 0 through 1023 and on most systems can only be used by system (or root) processes or by programs executed by privileged users." Their use is standardized, to perform a specific task using a specific protocol. For example, the FTP and FTP_DATA ports (ports 21 & 20 respectively) are used for FTP transfers, and all FTP servers expect FTP clients to use these ports in a standard fashion to establish connections and perform a transfer.
The Registered Ports are those from 1024 through 49151. "The Registered Ports are listed by the IANA and on most systems can be used by ordinary user processes or programs executed by ordinary users." Product and service developers register their products to use these ports. Applications using these ports may use standard or proprietary protocols. Examples are TCP/UDP ports 1214, which are registered for use by the KAZAA network. Rights to use these ports are not exclusive evidently as IANA indicates that TCP/UDP ports 4000 are used both by Terabase and ICQ.
The Dynamic and/or Private Ports are those from 49152 through 65535. These ports are for use in situations where the port on which a connection is made changes with each use or in private networks. Applications using these ports may use standard or proprietary protocols. For an example of dynamic ports, a client makes a connection to a static port, and the server examines a list of ports that it services and responds with an available port to be used for a transaction. An example of private port usage: an equipment manufacturer provides for Internet connections using a private port for firmware updates.
Using the IANA port list won't tell you exactly what is going on with a particular connection, but it can provide a clue as to whether it is legitimate or not. For example, if your firewall log indicates that a connection made by an application, whose executable you don't recognize, is using TCP port 1352, a check with the port list will show you that this port is registered for use with Lotus Notes. If you are using that application, then you can probably relax, but if not, it may be an indication that your computer is infected with some malware, and you should do some investigating.
Regards,
Hornus
