TCP/IP Tutorial and Technical Overview - IBM Redbooks

long, with the first two digits having specific meanings. See Table 14-1 and
Table 14-2 for descriptions of these codes.
Table 14-1 First digit reply codes and descriptions
First digit
reply code
Description
Table 14-2 Second digit reply codes and descriptions
524 TCP/IP Tutorial and Technical Overview
1yz Positive preliminary reply. These messages are usually informational,
and typically are followed by a message starting with a different reply
code.
2yz Positive completion reply. This indicates that the last client command
has completed successfully.
3yz Positive intermediate reply. This indicates that the client’s command
has been accepted, but that additional information from the client is
needed before the command can complete.
4yz Transient negative completion reply. This indicates that the client’s
command has failed, but that retrying the command might yield a
success.
5yz Permanent negative completion reply. This indicates that the
command has failed, and that retrying the command will not yield a
success.
6yz Protected reply. This indicates that the reply contains security-related
information.
Second digit
reply code
Description
x0z Syntax error. This indicates that a syntax error was encountered when
processing the client’s command.
x1z Requested information. This indicates that the message contains
information requested by the client.
x2z Connection information. This indicates that the reply contains
information about the control or data connection.
x3z Authentication. This indicates that the reply is part of the logon
sequence, or some other authentication sequence (such as TLS
authentication).
x4z Not in use.
x5z File system information. This indicates that the reply contains file
system information relevant to the last client command received.