ftp many pasv commands?

[Shwick2]

I was monitoring some ftp browsing and noticed that for each directory I clicked a new pasv command was sent to the ftp server.

This meant that a new tcp connection was created on a new port every time I requested a directory.

To ensure smooth browsing I have to allow a few new tcp connections per second in iptables.

Is this how the protocol was built, or do I have vsftpd set up wrong?

[linux_tech]

To make sure vsftp is running try this-
netstat -a | grep ftp

In vsftpd.conf you can restrict vsftpd data connections to a specific range of ports by using pasv_min_port and pasv_max_port.

[Shwick2]

Yes thanks, I know that it is running. I also restricted the port range from 55000 to 55100.

I'm just wondering why the client sends a new pasv command for each directory it browses? Is the client supposed to do that? It seems like a lot of new tcp connections.

[linux_tech]

These 2 articles help explain port usage for passive mode


didactiekinf.uhasselt.be/cn/slides/activevspassiveFTP.pdf

http://slacksite.com/other/ftp.html

[Shwick2]

Thanks for those, but I had already read http://slacksite.com/other/ftp.html.

I guess that means that any time any command is sent from the client to the server, be it a request for a directory listing or to download a file, a new pasv command is sent from the client to the server.