234 Security data exchange complete. RFC 2228 specifies that a server may prohibit the client from reissuing the AUTH command in order to establish new authentication, but provides no reply code to communicate this. The size agreed upon is subsequently used during data transfers as a maximum bound on the size of each encrypted block. However, some protocol mechanisms have a minimum encrypted block size, and RFC 2228 doesn't provide a way for the server to indicate that the proposed block size is too small. The guidelines provided by RFC 2228 for the naming of new protocol mechanisms are somewhat vague, and as such are insufficient for the purposes of successful protocol negotiation as described in section 2.
Names are case-insensitive.
RFC 959 requires that while in active mode, all outgoing data connections from the FTP server must be bound to port 20, as a weak form of authentication. Because RFC 2228 provides more comprehensive support for strong, cryptographic authentication mechanisms, it has made the port 20 restriction for outgoing server data connections obsolete, and the restriction is hereby lifted. This entire memo is about security mechanisms. FTP Security Extensions.