FTP Protocol
File Transfer Protocol(文件传输协议)
client/server model
- client: initiates transfer(to/from remote)
- server: remote host
- maintains "state": current directory, earlier authentication, stateful
transport protocol - TCP
FTP - RFC 959 Port - 21
Two parallel TCP connections
- Control: exchange commands, responses between client and server (out of band control)
- Data: file data to/from server
| command | parameter | usage |
|---|---|---|
| USER | username | |
| PASS | password | |
| LIST | return list of file in current directory | |
| RETR | filename | retrieves(gets) file |
| STOR | filename | stores(puts) file onto remote host |
| status code | introduction |
|---|---|
| 331 | Username OK, password required |
| 125 | data connection already open, transfer starting |
| 425 | can’t open data connection |
| 452 | error writing file |