The File Transfer Protocol (FTP) has a very long history@ and despite the fact that today other options exist to perform file transfers@ FTP is still in common use. As such@ in situations where some client computers only have IPv6 connectivity while many servers are still IPv4-only and IPv6-to-IPv4 translators are used to bridge that gap@ it is important that FTP is made to work through these translators to the best possible extent. FTP has an active and a passive mode@ both as original commands that are IPv4-specific and as extended@ IP version agnostic commands. The only FTP mode that works without changes through an IPv6-to-IPv4 translator is extended passive. However@ many existing FTP servers do not support this mode@ and some clients do not ask for it. This document specifies a middlebox that may solve this mismatch.