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Passive File Transfer Protocol

Passive File Transfer Protocol definition

Passive File Transfer Protocol, or passive FTP, refers to is a mode of communication in the FTP where the client establishes both control and data connection to the server. It is passive, because the server awaits for the client to specify where it should establish the data connection.

See also: data transfer, secure file transfer protocol

The difference between the passive and active File Transfer Protocols

  • Connection. In passive FTP, the client initiates both control and data connections, while in active FTP the data connection is handled by the server.
  • Firewalls. Because active FTP requires configuration on client-side firewalls to allow incoming connection from the server, passive FTP is considered to be more firewall-friendly.
  • Ports. Passive FTP uses a random port for data connection, which requires broader rules on server-side firewalls. An active FTP typically uses port 20 for data connection, making server configuration more straightforward.
  • Popularity. An active FTP has always been more popular, but in recent years the popularity of a passive FTP has been growing since it’s more compatible with modern network configurations.

Passive File Transfer Protocol use cases:

  • Home Networks with NAT. Most home networks today use NAT (Network Address Translation) for sharing a single public IP address among multiple devices in the household. But it can make it difficult for an outside server to initiate a connection to a specific device Passive FTP sidesteps this problem by having the client, which knows its internal network layout, initiate all connections.
  • Corporate and private networks with firewalls. Firewalls are often set up to block unsolicited inbound traffic. With the active FTP, the server tries to establish a data connection to the client, which may be perceived as unsolicited and thus blocked by these firewalls. Since the client establishes all connections in a passive FTP, it works better in these settings.
  • Web Hosting and Cloud Services: Many web hosting providers and cloud services use a passive FTP for their FTP services.
  • FTP Clients: Most modern FTP client software defaults to a passive mode due to its higher likelihood of success in varied network environments.