The TCP port of the role, the vulnerabilities and the operation of the detailed analysis-vulnerability warning-the black bar safety net

TCP port: the role,vulnerability,and operation in detail analysis In the Internet, we often see the“port”of the word, also frequently used port numbers, such as in the FTP address behind the increase of“21”, and 21 indicates the port number. Then the port in the end what does that mean? How do I...