Tyro studies hall: The two working patterns of analysis Ftp agreement

Tyro studies hall: The

The two working patterns of Ftp agreement:

FTP is a kind of data agreement transmited ( File Transfer Protocol), its connection

Following explanation

Under active pattern( the

FTP client opens the request of port 21 of call FTP server of TCP port of a random choice to establish connection. After completing Three - Way Handshake, connection is established successfully, but this is the establishment of order passageway only.

When the two end times of need to deliver data information , client tells server through

Then, server establishes data connection with port 20 and TCP port that client informs just now. Pay attention: Joining direction go to client from server, in TCP divides into groups can have a SYN flag.

Then, client can return a tape the confirmation of ACK flag to divide into groups , and completes another Three - Way Handshake process. At this time, data connection then can be established successfully. Begin data to deliver.

Under passive pattern:

FTP client opens the request of port 21 of call FTP server of TCP port

When the two end times of need to deliver data , client sends a PASV command

Then, server chooses a TCP port like the 2th step of above-mentioned

Then client uses the another call of TCP port TCP port that server informs

After server confirms , returning to send

Begin data to deliver. In reality is usedGo upFireFTP server, or set up FTP server in client side! Passive mode( abbreviation PASV) is used to land to set