What is PASV Mode FTP in Computer Networking?

Definition: PASV is an alternative mode for establishing File Transfer Protocol (FTP) connections. PASV mode is designed for FTP clients behind firewalls.

PASV mode works by allowing FTP clients to initiate sending of both control and data messages. Ordinarily, only FTP servers initiate the data requests. Because many client firewalls reject incoming messages like these FTP requests, PASV mode makes FTP "firewall-friendly."

Most FTP clients, including Web browsers like Internet Explorer, support a PASV FTP option. However, configuring PASV on the client doesn't guarantee that PASV mode will work, as FTP servers may choose to deny PASV mode connections. Some network administrators disable PASV mode on FTP servers because of the additional security risks PASV entails.

Also Known As: passive mode FTP

Examples: To set the PASV option in Internet Explorer, check the "Use Passive FTP" box in the Advanced tab under Tools/Internet Options. This option will not work with older FTP servers that do not support PASV. Also, PASV bugs have been found in FTP servers and firewalls, so this option is not 100% reliable.