FTP Sequence Diagrams

Here we explore the sequence of interactions in a typical FTP (File Transfer Protocol) session. Individual sequence diagrams for interactions on Port 20 and 21 are also included.

The complete sequence diagram can be divided into the following steps:

DNS Query to obtain the IP address for the FTP Server
FTP Telnet connection setup and login. (USER and PASS commands)
Obtaining a directory listing (PORT and LIST command)
Changing directory (CWD command)
Downloading a file using FTP get (PORT and RETR command)

FTP sequence diagram

The complete FTP session flow with port level details.

FTP session overview

FTP session examined at host level.

FTP port 20 (data)

FTP data transfer session on port 20.

FTP port 21 (control)

FTP control messaging telnet session on port 21.

FTP context diagram

FTP session showing the interactions between different entities