Working with a number of FTP servers, several include CLNT in their response to FEAT. However, checking the IANA list of registered FTP commands and extensions, CLNT does not appear. Monitoring various FTP sessions, it seems it is being used to identify the FTP client. Where was the FTP extension command CLNT established/defined?
1 Answer
While it is commonly used, it's not defined anywhere, afaik.
The CLNT has been added to ProFTPD server recently.
Note how it is referred to in its release notes:
Support for the common CLNT FTP command.
Comparing to for example:
Support the HOST command (see RFC 7151).
(emphasis mine)
answered Jan 14, 2016 at 15:18
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Here's an RFC that talks about the CLNT as well just in case you find it helpful in understanding protocol wise in addition to what Martin provided: RFC 3659... see section 7.8 and down for parts that may be relevant. I know this was published in 2007 but may help in understanding a little better what it's a part of
MLSx. Commented Jan 14, 2016 at 15:27