Hi list
Another question from me. Why do I see 3 TCP (1 control and 2 data) connections for my FTP download instead of the usual 2 connections (1 control and 1 data)?
This is what I usually get from my captures:
On control connection (port 21):
Login to server
Access file folder
Request for file download etc
The last command I get before data connection takes over is 'FTP response 150 opening binary mode data connection for ftp_sco_com.tar'. Then right after that on data connection (port 20), the download begins after handshake.
So I only have 2 TCP connections.
However, of late, there's always an extra data connection created everytime I did the download.
On control connection everything was fine, however, I noticed that the last command I got before the first data connection took over was 'FTP response 150 opening ASCII mode for /bin/ls'. Then the first data connection took over,
managed to send 56 bytes of data then immediately sent a FIN (and ACK,FIN by client). The content of data was the file name ftp_sco_com.tar.
After this happened, control connection continued to request for the file download and I finally got the 'FTP response 150 opening binary mode data connection for ftp_sco_com.tar'. The second data connection took over and the download begun as normal (on different client port).
So I have 3 TCP connections.
I don't have a clue why the extra data connection was created, and why it was on ASCII mode etc. To me, this data connection was a little bit 'premature', it seemed to be interrupting the process.
Hope anyone can give any ideas. By the way I set the transfer type to Auto in FileZilla.
Thanks
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