You need to understand Transport Control Protocol (TCP). Ports are a parameter of the TCP. There are many different services that can run using TCP as the mechanism to get data from one place to another. TCP keeps these services separate from each other by assigning a unique "port" to each service. Since the "port" parameter is a 16-bit field, there are 65,536 possible "ports" or services. Some of these, such as port 0, are reserved and not used.
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