Understanding FTP (a collection of useful links)

The File Transfer Protocol (FTP) and Your Firewall / Network Address Translation (NAT) Router / Load-Balancing Router

Wikipedia: File Transfer Protocol

Active FTP vs. Passive FTP, a Definitive Explanation

The FTP2.DetermineSettings Method

Issue when an FTP Server is behind a NAT Router

FTP Blockers – TCP/IP Port Filtering and Anti-Virus

Deep Inspection Firewalls and Passive FTP (also known as Stateful Inspection Firewalls)

Issue with Checkpoint Firewall and FTP

Active vs. Passive FTP

Port Range for Passive FTP?

WSAEWOULDBLOCK when trying to establish FTP2 Data Connection in Passive Mode with SSL/TLS

Running out of Ports for FTP Data Transfers