- Passive FTP mode. PASV is a means to get around a problem where a firewall
will block FTP communications. A firewall
protecting a client will allow outgoing connections but block incoming ones.
The issue with FTP is that whilst the client initiates the initial
connection the server then allocates the port to use for data requests - and
this is then blocked by the firewall. which is then blocked. PASV allows the
client to initiate both the command and data requests and because this is
initiated by the client the client's firewall does not block it.
For more information see:
- http://slacksite.com/other/ftp.html - Extensive article covering active and passive ftp.