FTP NAT Traversal

Techniques for establishing FTP data connections through NAT devices and firewalls, which is complex because FTP embeds IP addresses in protocol messages. Solutions include passive mode (client-initiated data connection), Application Layer Gateways (ALG) that rewrite embedded addresses, and the EPSV/EPRT commands that extend passive/active mode for IPv6. Misconfigured NAT or missing ALG support is a frequent cause of FTP connection failures.