TOPS-20 Telnet and Port Forwading issue

Peter Coghlan cctalk at
Tue Dec 13 14:01:29 CST 2016

> It's the SGA (suppress go-ahead) negotiation that's necessary to avoid line
> mode.
> Many telnet clients don't try to negotiate any telnet options if you
> connect to a non-standard port, because they assume that you're talking to
> something other than a telnet server, and that you therefore want an 8-bit
> transparent connection with local line editing. Examples would be to telnet
> to an SMTP server, FTP server, etc. for testing purposes.
> A telnet client that has that behavior but no provision for overriding it
> is defective, and should either be fixed, if possible, or deleted with
> prejudice.

My telnet client works just fine for testing SMTP servers etc.  I suspect
that it only decides to issue the SGA on ports other than the standard telnet
port when the server at the other end has already revealed that it is a telnet
server by sending out some telnet negotiation from it's side.

(I do recall a customer once insisting to me that I would not be able to use
 a telnet client to connect to his SMTP server to test it because the two
 aren't compatible or something.  At the time, it was something I did every
 day of the week but there was no convincing him.)

Peter Coghlan.

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