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Re: Telnet and FTP to Historic

Dave Cridland <dave@cridland.net> Thu, 03 December 2020 11:47 UTC

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From: Dave Cridland <dave@cridland.net>
Date: Thu, 03 Dec 2020 11:47:31 +0000
Message-ID: <CAKHUCzyB2pbxCg0hmJY5kFexLU2HHe3y-i7=3=YzKpCpBPmHWw@mail.gmail.com>
Subject: Re: Telnet and FTP to Historic
To: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
Cc: "ietf@ietf.org Discussion" <ietf@ietf.org>
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On Thu, 3 Dec 2020 at 11:39, Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
wrote:

> Christian de Larrinaga wrote:
>
> > there are times when having telnet to test a mail server / email
> > address is helpful?
>
> Yup. In that sense, all the ASCII based protocols are
> telnet servers.
>
>
This isn't true, in point of fact. FTP's control connection *is* based on
TELNET, but SMTP, HTTP, and others are not.


> Actually, when I teach ASCII based protocols (ftp, http, etc.)
> to students, I let them use telnet clients to access servers
> manually.


A conformant TELNET client implementation can (and maybe even will) send
IAC commands over the link, which will confuse HTTP and SMTP, and quite
possibly mildly surprise non-conformant FTP.

I'd suggest you use `nc` instead of `telnet` to avoid this risk.

Dave.

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