问题
Why is 22 the default port number for SFTP? Is there any specific reason for this?
回答1:
It's the default SSH port and SFTP is usually carried over an SSH tunnel.
回答2:
Why is 21 the default port for FTP? Or 80 the default for HTTP? It is a convention.
回答3:
From Wikipedia:
Applications implementing common services often use specifically reserved, well-known port numbers for receiving service requests from client hosts. This process is known as listening and involves the receipt of a request on the well-known port and reestablishing one-to-one server-client communications on another private port, so that other clients may also contact the well-known service port. The well-known ports are defined by convention overseen by the Internet Assigned Numbers Authority (IANA).
Source
So as others mentioned, it's a convention.
回答4:
Not authoritative, but interesting: 21 is FTP, 23 is telnet. 22 is SSH...something in between (that can take the place of both).
回答5:
Ahem, because 22 is the port number for ssh and has been for ages?
来源：https://stackoverflow.com/questions/6266177/why-is-22-the-default-port-number-for-sftp