Keep EPSV ALL scoped to its FTP session

An EPSV-only commitment cannot be undone by quietly falling back to another setup command.

• After EPSV ALL the server MUST reject data-connection setup commands other than EPSV, including EPRT, PORT and PASV. This is a method restriction in that session, not a claim that every EPSV argument is valid or every later transfer succeeds.
• A client expecting only two-way transfers SHOULD issue EPSV ALL as soon as possible. SHOULD is a recommendation; the separate same-two-machine EPSV usage rule is MUST.
• If a three-way FTP transfer becomes necessary after EPSV ALL, a new FTP session MUST be started. The old session does not need to be depicted as closed; its commitment is not cleared in place.
• The illustration does not prescribe a numeric acknowledgement code for EPSV ALL or a particular rejection code for later disallowed methods. A later ordinary EPSV success uses 229. Authentication, authorization and confidentiality remain separate.

Documentation addresses and chosen listening ports. Each chapter is a separate bounded example; FTP authentication, authorization, file commands and transfer replies are not a complete FTP implementation here. EPRT/EPSV provide no encryption or guaranteed reachability.