Which of the following communications uses the well-known port number 2 1?

FTP .

According to Baidu's educational materials, which of the following communications uses the well-known port number 2 1? A. FTPb. Song Seung Heon; C. SMTPD. HTTP Answer: A: FTP.

Port 2 1 is mainly used for FTP (file transfer protocol) service. FTP service is mainly used to upload and download files between two computers. One computer is used as an FTP client and the other computer is used as an FTP server. You can log in to the FTP server by anonymous login and authorized user name and password login.

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