Control Connection Negotiation with Implicit FTPS

The client connects to the TCP port dedicated to Implicit FTPS, but MUST NOT expect the greeting message immediately. Instead, the client MUST proceed as if it had sent an AUTH TLS message and received a positive reply in response. The TLS session negotiation MUST follow the sequence specified in [RFC4217].

After TLS negotiation has completed, the client MUST NOT send PBSZ 0 and PROT P messages. Instead, it MUST assume that the server successfully processed PBSZ 0 and PROT P messages and sent a positive reply. Implicit PROT P messages will switch the FTP session to the mode requiring secure data connections as specified in [RFC4217]. The client MUST maintain the internal state about the data connection mode based on the implicitly assumed PROT P message.

After TLS negotiation the client MUST receive the connection greeting message as specified in [RFC959] section 5.4.