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Re: tcp connection

----- Original Message -----
From: Russell Coker <russell@coker.com.au>
To: Chris Wagner <wagnerc@plebeian.com>; Debian ISP List
Sent: Friday, June 23, 2000 5:18 AM
Subject: Re: tcp connection

> On Wed, 21 Jun 2000, Chris Wagner wrote:
> >At 02:25 PM 6/20/00 +0200, Russell Coker wrote:
> >>They don't use NVT.  The TELNET protocol is not running
on (for example) a
> >>web server.
> >
> >Yeah but the NVT settings have to be negotiated for each
side to talk to
> >each other.  If I telnet to an Apache webserver on port
80, my telnet is
> No they don't.  If the server doesn't start NVT
negotiation then nothing
> happens.
> >going to negotiate NVT with whatever's on the other end.
Both sides have to
> >agree to establish the connection.  Therefore, either
Apache or something
> >below Apache in the stack has to know about NVT.
Otherwise Apache would
> >tell me to go take a flying leap if I tried to telnet to
it.  What is my
> >telnet client negotiating with in this case???
> Telnet client negotiates nothing.  Text you type is sent,
but "\n" is
> replaced by "\r\n".  Text that is received is just
displayed as-is.
> As an experiment to find out how hard it would be for you
to determine this
> without asking the list I timed myself.  I determined that
in 121 seconds by
> running strace(1) on telnet.
> I tried using ltrace(1) to determine the same information,
but after 149
> seconds I realised that it was not the right tool and
would not be able to
> provide me with the information.  Ltrace displays the
values of pointers
> instead of the data it referrs to.  I could have used "-S"
which might have
> been more useful, but there's no point when strace(1) is
> Then I decided to solve it properly.  Firstly I read
rfc854 and rfc855 (the
> base RFCs on TELNET) which didn't clarify this issue.
Then I put a telnet
> daemon on port 23 and straced a telnet connection to it.
The telnet client
> started with sending a sequence of NVT protocol commands
to it which were
> responded to.  Then I put the telnet daemon on port 1000
and repeated the
> test, this time the telnet client didn't start sending any
NVT commands until
> after it had received some (the server had shown itself to
be a NVT protocol
> server not a web server or whatever else I may have chosen
to run on that
> port).  NVT is totally bi-directional so it could run
either way.  This took
> me 821 seconds.
> Chris, most people here would not be able to do what I
just did.  However I
> believe that you are able to do everything I did (although
it may have taken
> you a bit longer).  I think that you should be answering
questions of that
> nature not asking them.
> I often see questions that I don't know the answer to, and
research them for
> the benefit of the person who asked and everyone else on
the list.  It is a
> great way to learn about things if you've got some spare
time.  This is why I
> think that you should have researched and answered if
someone else had asked
> the question.
> Russell Coker
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